If you see me sitting in a transport gun positioned somewhere shooting at people, don't jump in a drive me off, usually into a tank shell that kills us both. I hate when people move my vehicle when I'm positioned in a good spot and killing people.
About medics, I've had many games where I'd stand right in front of a medic or support guy asking for healing or ammo and they'll just sit there and ignore me. So tempting to just kill them and get their attention that way. And i hate when I die by a medic and he doesn't revive me. I can understand if we're under heavy fire, but not in other cases.
Don't stand behind tanks. If someone shoots a rocket at me, my first instinct is to back up and if someone is behind me, they're going to get run over and I'm going to get ****ed at having a TK.
If you have one flag left, don't stand around it. Take whatever vehicles are there and split up, going for any flags. Some people just don't seem to understand the concept of flag control and how important it is.