What was your most intrusive thought?

Whenever i have a knife and see a thick electrical wire i have to stop myself from "just testing" what would happen if I cut into it. I work with 400v ac on a construction site a lot and I know what would happen lol.

Mine has been to slap a stranger. I want to know, what will happen after that?
- I did that accidentaly once. We were visiting Scotland and I tried to point out something and accidentally slapped a woman straight in the face. She just cursed and looked at me strangely and walked away.
  
  At least you are a wizard and a pope, so you can lift the curse, right
  
  In college I was enjoying some recreational activities at a house party.
  Next to me on a couch was this kid who had like low grade cerebral palsey or something. Like, legitimately, he had those arm crutch things Walter White's kid had. Never asked what it actually was.
  Anyways, he laughs at something and leans back on the couch. And accidentally does one of those back punches like Bruce Lee. Like, where someone sneaks up behind him and he just hits them with the back of his fist without looking.
  Anyways, dude gets me straight in the nose, doesn't stop laughing, gets two inches from my face and screams
  You just got punched by a fucking cripple
  And just absolutely died laughing.
  He was a cool dude, and that was probably the only time he's punched anyone in his life, and it was absolutely an accident. But it was just hilarious how he rolled with it

I often get the urge to steer into groups of pedestrians and cyclists or knocking over small road signs
Never did it obviously. my car would not survive that anyway.
Probs just Tetris effect from the hundreds of hours I spent playing GTA when I was younger. I'd always do that shit
- Bill Burr had a bit on it.
  
  oh my god I can't breathe
  fucking love billy burr
  
  Thpppppp

At my last workplace there was a central staircase with a gap in the middle through the whole building.
I very often had an intrusive thought of jumping down 4 stories.
It came even more often when one of the lights inside this gap started flickering and I could have taken it down with me.
- I get that urge time I use a helical staircase with a human (or larger) sized central air gap. I think it's a niche form for High Place Phenomenon... maybe because I watched too much Batman (TAS) as a kid.

I get bad short thoughts about how I could easily end so many personal relationships with a quick random punch to the face. Pick the right person and you could be ostracised from your whole family.

Whenever I pick up my knife my brain says, "what if I just stick this into my belly?"
They say your brain imagines these scenarios so that you can try to avoid them, but the more you learn about trying to wrangle your brain the more I think the brain is just a dick sometimes.
- They say your brain imagines these scenarios so that you can try to avoid them
  Not quite.
  Like, there's a scary amount we don't know about the brain and how it works.
  But I think it's a little different than you said. It's the brain trying to figure out how it would deal if that happened.
  Like, you avoid stabbing yourself by not stabbing yourself.
  But your brain is evaluating if stabbing yourself so you can practice surviving a stab wound would be a good idea.
  Which, sounds crazy, untill you realize most of what humans do for fun involves tricking our brains or bodies I to think we're in danger. Hell, even the drive to "play" is just tricking us into exercising so we're stronger if we do have to fight.
  Even tickling is just teaching kids what parts to guard in a fight.

I used to ~~rummage~~ ruminate often, meaning that many old conversations, arguments, and aggressions lingered in my mind for days and would upset me very much. I went to a psychologist and she was incredibly dismissive so I had to deal with that on my own because I felt ashamed to go anywhere else. Thankfully, I don't have them anymore or as much as I used to.
- I think the word you're looking for is ruminate. The word comes from ruminant animals like cows, who partially digest fibrous plants, regurgitate them, and "chew cud". Which is what we do when we regurgitate negative memories.
  My tool, which works for me but i am not a mental health expert, is this:
  When i find that I've entered a ruminant thought cycle, I'll start asking these questions and working through it logically
  Does this memory have something beneficial to teach me in this moment?
  Can I learn any more from this memory?
  The moment is in the past, and I'm alive here and now
  I am the only one who still remembers
  This memory is no longer useful, I will think about something else
  I'll think about something now, because I'm alive now
  I'm sorry your psychologist was ineffective. A good one can be hard to find
  
  That's a great comment. I go though basically the same steps with my constant flow of embarrassing and/or sad memories
  If they're useful then maybe I should explore this thought for a little longer, or try to speak with someone
  If I have nothing to gain from it and it's just making me cringe or sad I try to do something else to distract myself
  It's important to not shut these memories down immediately. Some memories really need to be explored in order for you to properly leave them in the past. And you can bottle up a bunch of emotions if you refuse to think about thoughts that come to you constantly.
  
  the word you’re looking for is ruminate
  I do! I can't believe I used the wrong one, that's embarrassing. Thanks for the tips and the correction!
- I'm sorry that you had a bad experience with your psychologist.
  If I can point out one thing that might help you is that these thoughts largely come from an evolutionary trait called Negative Bias
  Negative Bias is the disproportionate focus on bad events and/or memories compared to good events.
  It applies to a large range of memories and our ability to perceive danger. Evolutionary it makes sense because our embarrassing memories makes us afraid or unwilling to behave in a way that the social group doesn't like.
  You can imagine when humans lived in societies in small groups of 30 people, that disrespecting someone could get you kicked out of the group and potentially starve to death in the wild. So there is a very strong evolutionary pressure that made your brain evolve to avoid repeating bad scenarios
  Your constant embarrassing, sad, or traumatic memories are your brain reminding you over and over not to be in that situation again.
  Unfortunately your brain didn't evolve to be happy. It evolved to survive.
  All I wanted to explain is that these memories are not your fault. Don't feel like you're any different because you have bad memories constantly. Accept that your brain will do what it is programmed to do and learn how to work around those tendencies.
  And I could recommend trying another psychologist. I'm also available to chat if you'd like. Cheers 🙂
- Please don't give up on finding a mental health care provider who works for you! If it helps, think of it like shopping for any other product or service; you want to pick out food that works for you, clothes that fit you well, electronics you can use well, the right beverage you're in the mood for in the moment, etc. and finding a psychologist who provides the psychological care that works for you as an individual is just as important.
  It's very important to remember that not jiving well with one psychologist, therapist, etc. is not in any way a failure on your part. Sometimes someone just isn't the right service provider for you, and that's nothing you need to be ashamed about.
  If you are getting a builder to work on your house, a mechanic to work on your vehicle, and such it's perfectly normal to consult with more than one person before picking out who you think is the best for for the job and to change providers if one isn't working out, and your health is no less important to get the right person to work with you on.
  I'd go so far as to say that the vast majority of people who use mental health providers have encountered one or more that just weren't right for them, and I certainly count myself as one of those clients. There's absolutely nothing wrong with shopping around for someone who works out better for you.

Toddler related as well. Wanted to slam his face into the edge of the sink until the screaming stops. It was pretty close a few times.
- This is why I will never have kids.
  
  Yuuuup same.
- This is probably normal. Kick it like a soccer ball, slam it into ground, throw out through train window while moving,...
  
  Always felt like stabbing footballs when practicing juggling. Knowing I felt that kind of anger towards inanimate objects was a big reason not to have kids. Destroying your own property is fine. It's just property. A kid though...

Most intrusive?
It think it’s probably a relatively common one: you’re at height, with access to the precipice, and your brain starts entertaining the possibility of jumping. Nothing compelling about it, in fact my rational brain always tells the stupid part “WTF, bro…” but nonetheless, the thought exists.
Occasional other random thoughts pop in to my head on rare occasion, but for some reason the “jump” one is the most common and the most irritating.

I should just go on a road trip again. Every time I get on the highway by myself, and I see that open road, I think about how I could just go and take another road trip.
Fortunately, I got a trip to the grand canyon lined up for this fall, if all goes well.

That I'd somehow developed Alzheimer's in my 20s

Jumping in bodies of water and letting the water carry me away. It's a weird mix of "appel du vide" and the urge to be cleansed.

Whenever I see game (and some domestic) animals I instinctively look at them as food and trying to find a way to kill them right then and there. Just the outline of the flesh is enough for an instant plan from slaughter to plate.
- One of your ancient ancestors is like "this guy's the one, time to egg him on again"

My most common thought of all time or my most common that appears unprovoked?
My most common thought of all time is, just generally, about how mentally misguided humans are in general. In my experience, people predominantly have an "ask questions later" approach to things, and then when they do finally "ask the question", it's "how do I excuse myself". My whole life, and everything I've learned from history, is shaped by this, and they hate pushback. If humanity killed someone for agreeing, in time, would they be remembered as a philosopher or a crazy person since inclination rules?
My most common thought that appears unprovoked is similar, it deals with the situations I've been witness to in the name of what I described and trying to think out what the implications actually are and what would be in the best interest of each situation. I recently watched a show about a guy who built 100 houses for people in an impoverished country, and people reacted to this act of charity by complaining he was continuing colonialism. Sometimes "I can't even" is a perfect mood descriptor.