Top 3 together with the Fighting game community and RPGs (especially JRPGs with the dub/sub war) are chock full of trolls. But if you wanna get specific on which franchises, I'd say Street Fighter and either Final Fantasy or Tales of... games seem to exhibit the greatest amount of trollism.
Given that CoD does attract pre-pubescent boys in swarms it is quite likely that a lot of these people are just mad at constantly losing and they are pros and all so it MUST be something wrong with the game. Fingers crossed they patch that something soon, eh? :)