It royally fucks me off when info boards get used as full screen adverts. Costa and McDonalds are particularly bad - I don't give a fuck about your 1998 Shockwave animated soft drink advert, show me the fucking menu!
I'm not bothered about "idle" screens getting used for adverts such as airport departure gates with no plane berthed, but it's incredibly frustrating when a screen has one job, that gets hijacked by adverts.