First off, a silly animation in a video game vs. an actual taunt to bully someone in real life is completely and utterly different. Any and all negative perception of such a ambiguous gesture in a VIDEO GAME is baseless and therefore in the end a mere assumption on the receivers end.
Secondly, the reason why most people mainly do it or at least why I do it to complete strangers isn't to piss off but rather just to playfully signal to the opponent 'tag you're it' or 'hahaha got you, come get me back!' Similarly to how everything in nature including us humans likes to play fight, compete, and have extra fun. This is just another form of that.
Finally, I used the words 'seriously' & 'come on now' not because I think you all are stupid but because I think you all are miss understanding and overreacting on the concept of 'in game taunts'.
Not buying your argument.
First off, your examples of "playfully signal to the opponent" are taunts. They're egging opponents on. "Come and get me" is a taunt. "Tag, you're it" is a taunt. It's fine with people you know, as they know you're just fooling around, but you cannot blame a complete stranger for getting annoyed by sand bagging. After all, seabagging is a substitute for the way people usually sandbag in other games such as shooters: squat over the downed opponent as if you were "going number two" over them. Again, to friends, it's a harmless joke, but you'd likely look like a jerk to complete strangers who don't know who the heck you are, and think you're a fun-ruining troll. It's fun to you, but the others may be legitimately be bothered and not get that you are joking around, and you can't really blame them with how sandbagging is usually percieved.
Next, just because the setting of the taunting is a video game doesn't matter. A taunt is a taunt, the message isn't warped by where you're doing it. Where did bullying come from in your argument, anyway? It's intentionally irritating people, aka trolling, not bullying.
I understand the popular opinion can occasionally be less justified, but I highly doubt we're overreacting. We react differently to things. Some people are fine with scary pranks, but others hate it, and that's fine. Some people laugh at getting their hair shaved as a prank, but others very understandably get ticked off. That's how we are.
@Demosthenes: That's not even taunting people. That's completely fine.