My top one is the butchery of the English language. The worst one is using "busted" to mean "broken". Even the news anchors are doing it -- talking about a "busted" water main instead of a "broken" water main. It drives me crazy!
The next one is parents who, when you speak to them about their child's behavior in class, yell at me instead of the child. Excuse me, but I am not the one misbehaving!