Quick primer on what is acceptable in TT games by the majority of players (not all, but most).
I will only address scrum and team scrum because that's what I play. BM, Team BM and CTF players feel free to post what you think is fair play in your games.

Indie Scrum
Camping is frowned up and not acceptable unless you're a demo or a noob. Vets eat campers for breakfast most of the time so it's just a nuicance more than anything. I personally enjoy making a camper look foolish so it's fine with me.
The real issues arise when someone who's been around long enough to know better decides to camp anyway.
It doesn't happen a lot but enough to raise a stink every so often.

BMing opponents is acceptable if they are either carrying the scrum or trying to grab the scrum. Shooting any opponents just because you can is annoying and a waste of time. That's what JFDNY and the Demo Attack idiots did all the time.

Diving with the flag is never acceptable.

Team Scrum
Camping is actually a smart and successful tactic in team scrum! I keep seeing newcomers to team play complain about opponents camping and I try to make it clear to them that it is all right to do so in team scrum. It's not good in indie scrum but fine in TS. Some players are awesome goaltenders (Lonewolf, Pharmeceuticals, Tally Ho).... Some are not.

BMing in team scrum is different than indie scrum. You are encouraged to shoot any and all opponents but only to the point of near death. The mantra is to keep them smoking....until you get close to the goal or scrum. There should never be a senseless killing. Timing is everything because of spawning. You don't kill an opponent chasing your teammate if it looks like your team is going to score because they might die and spawn in the goal before your teammate reaches it!!! DOH!!!

Diving with the flag is never acceptable unless you're surrounded by opponents near the goal and smoking badly.
Just kidding, even in that case you should not jump!!!

Those are just some tips....

Great tips there, might wanna add my name to goal keepers ;)

I love blocking people off and whilst they try and get past watch them fumble, Hilarious!