I'd argue that "teabagging" is probably the farthest thing from an adult celebration and is usually a sign that the player is underaged. That's just me though and may be indicative of my age. The adult thing would be to be as respectful as possible to the opposing party. I will say that the current generation of young adults is definitely lacking in maturity overall, and many of their behaviors border on childish.
God damn kids these days, always so loud and skateboarding on the sidewalk. Back in my days, we used to {/bow} before initiating a 1v1 fight.