Dude I hate it when people interupt me.
I also hate it when parents try to justify their children's actions rather than disciplining them until they have learned the right thing.
But my biggest pet peeve is when people ask me a simple question and I respond to them. They then proceed to ask another person the same question right after I just responded to them and that other person gives the exact same answer. It's almost like they don't trust me to give correct information. I know you might want different people giving you information for reliability, but why do you have to ask right in front me when you just asked? It makes me feel stupid and unworthy.