When you are choosing something in a supermarket, and someone comes up very close and snatches something in front of you off the shelf
Oh, shelf blockers do my head in. Choose and move on or stand back so others can see. Even worse when it's a couple who go shopping together.
People who you have spoken to socially at a gathering (work/neighbours party) at some length who then do not even acknowledge you next time you walk past each other. Just the awkward, "Oh, hi!", smile, not expecting a conversation. And, no, I don't think I'm that boring they're deliberately trying to avoid me 