At the checkout at the supermarket loading up the conveyor belt...guys stands behind me with his trolley and (while I’m bent over in mine so can’t see him) places the separator thingy down and starts quickly loading his things on to the belt.
Erm...I’m not finished?! I don’t know how much room I still need but he somehow did 😂 it left me piling stuff up on top of things as he’d left me no room. I gave him a dirty look but wasn’t assertive enough to point out his rudeness 
I know it’s a very small thing but still...What things irrationally annoy you?!