Can people tell sex of a dog just by looking at the dog?

I'm not pet owner and I don't spend much time around animals in general. (Don't get me wrong, I love them, It's just I know I would be a terrible pet owner.)

How common it is for people to see, let's say, a dog and immediately just know whether it's "she" or "him"? If two dog owners meet in a park, would it be awkward for one of them to misgender the other's dog?

Of course, I mean without looking at the "obvious" traits.

Are there behaviors that are typical for male/female pets outside the one directly related to mating?

I recognize that within the animal kingdom, the traits are not always clear, and I guess gender is quite more flexible than sex. I would be interested in both aspects.

What about cats or other animals?