Anyone who blocks the aisle at the grocery store, period. I don't care that you're five minutes deep into a mental comparison between brands of whatever. I don't care that your friend is there and you want to chat with them. I. Do. Not. Care. I am there to get my groceries and get the Hell out. If you want to be uninterrupted in your perusal/chat/whatever? Then stop leaving your cart in the middle of the goddamn aisle. I have zero compunctions about pushing your cart to one side or the other, and will, regardless of how much you glare or bitch at me for interrupting your precious whatever time. You interrupted my grocery time first.
*Empirical you, obviously.