Please. This type of stuff happens all the time. Hyper-competitive pampered athletes who continually have people around them shoving gatorade, towels, etc in their face during games.
Just happened to be caught on tape. You think KG's never sworn at a towel boy to get away from him? You think Pierce has never swatted a paper cup out of someone's hand when they offered him some gatorade?
Athletes get frustrated, they play a high-stakes game, and its part of the way things work that once and a while (or more often than not for these Celtics) you're gonna lose and get frustrated. Happens all the time.
Not saying it wasn't classless, just not unique.