I haven't run into nearly as many as I did on COD4 in the months leading up to MW2 being released. It was pretty ridiculous at times. They are good for some comic relief though.
One night earlier this year, while playing HC TDM on Crash, there was a kid talking non-stop crap in the pre-game lobby about how he was going to "pwn us noobs". Game starts and where does this kid end up? The top of the 3-story building by the chopper w/ a Barrett. Me and a teammate took turns picking this kid off and every single time, he just came right back to the roof. One guy even snuck up there using the ladder on the side of the building, stabbed him in the back, then hid behind the stairs, only to knife him when he came back 30 seconds later! About halfway through the game, I mentioned to my teammates that this kid has to be going ballistic right now and I switch to my class w/ Eavesdrop on it and grenade myself. Sure enough, the kid's going crazy, but only as a 10-year old can (saying "Gosh darnit!", "Mothersucker!" and "Bullcrap"). After the game is over and we're back in the lobby, we're all laughing our asses off at this kid as you can hear him throwing a full-on raging tantrum. The guy that knifed him on the roof even asked if he ever thought about trying somewhere else to snipe from and that the pile of bodies should've told him that it wasn't a safe spot to sit.
Just when things couldn't possibly get any better, we hear his mom yelling in the background things like "I can hear you all the way upstairs", "if you can't control yourself, then turn it off" and "you've been playing this stupid game all day...that's enough!". We hear the kid literally start squealing and his name disappears from the lobby. I laughed so hard, I nearly pissed myself. Easily the best thing that's ever happened to me in an online game...eva! lol