First off, these people like to start shit with people that even mention other gaming series that rival the Call of Duty series, mainly Halo, Battlefield, and Metal of Honor, and these battles set off fanboys of the other series, causing these "wars" between the two series.
Second off, they don't know how to enjoy the game right without arguing. About everything. But the two that are probably argued about most is when they get killed, or blaming lag.
If they get killed, these fanboys scream random curse words and insults, just because they died. In a videogame. Take games waaaaay to seriously and act snobby.
And when the game lags, which, honestly, happens a lot to Call of Duty, they blame it for something that had happened during or previously to it. If they were killed during it, then they will get mad or/and ragequit.
Then, there are many different kinds of these fanboys, not all that I will name, but mainly the popular ones.
Kids- Many kids like playing Call of Duty because thats the "family game" nowadays. And by kid, I mean twelve and under. Trust me, you will get a lot of these. Not all of them are fanboys, just really annoying.
Assholes-13 and up. Have some of the most over used insults and comebacks ever, are just generally dicks.
Try-Hards- These people take the game the most seriously out of every one, and complain the most.
Me-"Man, this looks really good. I can't wait to play it*
Fanboy Reply-"BATTLEFELD SUX DICK MW3 FTW U FAG"
Me-"Uh, what the fuck? If you don't like BF, then you don't have to comment on it"
Fanboy- "B1TCH I DONT CARE ABOUT UR RESONING, BATTLEFIELD 3 IS TERRIBL JUST LIEK UR MOMS PUSSY"
Me-"Have you played Battlefield 3? OR Modern Warfare 3? Nope, because neither are out yet. All your saying is biased opinions, mother fucker. You Call of Duty Fanboys piss me off"