I only taunt if I'm playing with friends and we both acknowledge that taunting is allowed. At that point, it doesn't feel so unsportsmanlike, just us displaying our often-times cruel sense of humor to the other one. However, if a friend doesn't like it or if I'm playing with random people I don't really know, then I won't use it. In the former case, it is unsportsmanlike, and in the latter case, they'll likely take it as unsportsmanlike conduct, as they probably wouldn't understand any of the humor behind it and how I'm not that kind of person.
As far as teabagging, let me just say this: If you see me teabagging, assume my account was hacked! I can't stand it, at all. It is the most childish-looking, pathetic way I can think of to demean an opponent, and few things give me as much joy as to kill the guy currently teabagging my corpse. Not to mention, the people I know who teabag are a constant reminder to me of why the FPS community is right up there with MOBA and fighting communities in terms of how truly unpleasant their players can be to play with at times.