I hate people who cut in line.
Ok, here's a big one. You're in a store. There are 2 registers. Only one is open. Everyone gets in the one line and waits and waits. The line slowly moves along. Some people have been waiting for 15 minutes or more. The other register opens and the people at the END of the line who have only been waiting a minute or 2 rush over to that register. The cashier should ONLY take the next people in the first line who have been waiting the longest. It should be a rule! It should be a law! This makes me want to take a flame thrower to the store.