Camping in an FPS is the practice of being a mega-monster-douche who can't get kills, so he/she/it stays in the same spot for a long time waiting to pick out those who have strayed too far from the pack. Camping is acceptable only for snipers.
There are worse crimes, though. I have an entire hierarchy which I will post here.. Because I'm bored.
The absolute worst is glitchers/hackers. I didn't even include them on list. I instead expressed my deep hatred for them in any online FPS and I have a 'special treatment' for the first hacker/glitcher I meet in real life.
1. Using only the noob tube to gain kills.
2. Camping when not a sniper.
3. (For recent CoD games) Using Commando Pro, Marathon Pro, and Lightweight Pro with a 'Tac-knife' and running around using only said Tac-knife to gain kills.
4. Pre patch Model 1887's with Bling, Akimbo and FMJ (though this is now obsolete.. Except for the fact that they're still fucking cheap)
5. Care Package Glitchers. They're technically glitchers and don't belong on this list and instead in my torture chambe- I mean.. Nevermind. But they've become such a big part of CoD gameplay (I guess this list has turned into a CoD based list, imagine that) that even after nine patches, it still isn't fixed. I sometimes wonder if the devs put it in as a feature and not as a missed glitch (among many).
Also, these are in no particular order, I hate them all the same.