If you have blown your whistle then you can say that this is a DB UNS. Otherwise it is a live-ball foul.
I suspect most, if not all, are well aware that "Showboating" has become an ever expanding, unnecessary & potentially threatening situation, not to be confused with genuine (but reasonable) jubilation, that may provide fuel to unnecessary, and troubling, reaction. It would seem that simply eliminating the frequency/drama of such consistently escalating behavior, is far more beneficial (to the sport) than repeatedly dealing with, and unfortunately addressing it.
Addressing these situations initially, with both the player(s) and BOTH Head Coaches initially, that such behavior is unacceptable & repetition will be subject to serious penalty, although minimally time consuming, once recognized should prove an eventual deterrent, beneficial to the Sport.
Allowing this nonsense to exist, unchecked, is INEVITABLY likely to expand and further threaten the principle of respectful, and indeed friendly, competition and mutual sportsmanship so important to the, history and purpose, of the game.