ignorant people. ie. all gamers wear glasses and are morbidly obese, only 5 year olds play pokemon, sports scholarship is just as impressive as a genuine scholarship, only consumerist 10 year olds play CoD, sci-fi/fantasy is stupid, etc.
also, condescending douchebags. ie. "THE LAST GOOD COD WAS 4", "PC GAMING HAS, IS, AND ALWAYS WILL BE BETTER THAN CONSOLES. NAME 1 GOOD GAME EVER ON A CONSOLE", "I don't spend tons of money on clothes from Hollister like all of those conformists... I spend tons of money on clothes from HOT TOPIC!", "Inception was WAY better than Toy Story 3/Scott Pilgrim/The Social Netwrok. you just don't GET IT.", "the US has one of the WORST GOVERNMENTS EVAR!"*, etc.
*note: they would not be allowed to say this in a country like China. they would be arrested.