The act of teabagging by itself is not funny, the salty reactions from many of the people on the receiving end of a teabag is what makes the entire thing funny, people get so easily wound up by it.
I've played dozens of FPS games, and I've never seen any community get more riled up about teabagging than the Destiny community does, people lose their shit over it. The amount of hate mail I've gotten after a crucible match is ridiculous, I once received a near essay long, multi paged message detailing how it was disrespectful and arrogant for me to teabag because I regularly finish at the very top of the leader board, seemingly implying that if I was a shit player than teabagging would be ok, something which gave my friends and I a good, long laugh.
This and more is why I will continue to teabag until the Destiny servers go offline for good, because if I'm going to be stuck playing this game with a community this hilariously uptight for the next 10 years, then you can be damn well sure that I'm going to take the complete mick out of it every step of the way.
Note:I'm not talking about DestinyGAF, but the rest of the online community.