As I mentioned, I only really find going on about being happy Not Cool when it feels put-on or fake; lots of people act a great deal more happy than they actually are because they see it as socially useful, or (if they are genuinely happy) express it principally for that reason as opposed to the genuine need to express it; it's a phenomenon as pronounced and as annoying in RL as online. People who are consistently chirpy on principle fall into this category. 'Twere prophanation of our joyes, and all that stuff. Of course, it can be a very fine line, heavily reliant on individual judgement, and whatever you do you're likely to piss someone or other off anyway; I personally haven't seen you do anything I'd consider flaunting. Being unhappy for social effect is, of course, just as bad and just as annoying.
The remainder of the cause of people being pissed off about you acting happy is just envy, in which case they can go to hell.