Old timers and/or chairsofters who chronically and needlessly hate on various things in an unproductive and unhelpful manner, or go out of their way to hate when they could instead be helpful ambassadors. People who are perennial jerks to everyone whose life path up to that instant didn't precisely match theirs, so if the stuff y'ought-to-know is even slightly mismatching, hellfire ensues. Happens here every day, not nearly as much on the field where it's hard to do that to someone's face.
List of stuff people hate on:
1) New people, new players, expansion of sport
2) Brands of guns or brands of gear
3) Types of guns (some hate on AEGs, some hate on GBBs)
4) People whose only crime it is to have played call of duty and to have gotten excited about military/tactical/gun/etc stuff
I'm guilty of #2, #3, and #4 . Trying to get better at it