I've only seen it going on twice but I don't really play on free for all much, I'm a domination lover. The ones I saw at it were on Domination, in Terminal and Wasteland. Which I thought was an odd game mode to be boosting in. After thinking about it a bit it kind of made sense. With everyone focused on the flags there are lots of quiet, out of the way corners to hide in and do their dirty, sinful business.
Not even close to getting one. To be honest, I've given up playing it seriously. It just takes too long to get to prestige mode and I got bored. I just dick about now. Something I love doing is sneaking up on my team mates as they snipe and slashing them with my knife, not in hardcore though. The reactions are well funny. They think the enemy is after them and take evasive action. Its best if you find someone on a rooftop, a lot of the time they just blindly jump off to escape.
Another fun one for snipers is to sneak up on them while they are looking down the scope then quickly run in front of them and crouch/ stand up while shouting "How you like m'nuh? How you like m'nuh?".
Good clean tea bagging fun.
Mis infomation is always good too, de-railed is esspecially good. Get a good high vantage point then find one of your team mates. Then, when there no enemies are around tell them "Killerdude06, you got one round the side of that train to your left". Observe his reaction, it'll probably be a time wasting sneak around. After he rounds the corner with all guns blazing, say "You missed him, he just went round the other way!". See how long you can get someone to to hunt a non existing enemy. The opposite of this is funny to, telling someone they are all clear when there is actually a ton of baddies round the corner.