It's the worst when the people that sit behind you in lecture talk the whole time. They think that they're the only ones that can hear the conversation, but really, the next 3 rows can hear them too, and it's very distracting. I remember last year in Psychology, Kyle said something to the people behind us, and they probably made fun of him after. It really doesn't matter what you say to these people, because even if you are polite, they will still think whatever you say was bitchy.
On a side note: an old man in front of me made a complete stop at a crosswalk with no stop sign, and no pedestrians or bikers crossing. Old people should have to retake their license test.