The terms and conditions say that your account can be changed for any reason, including pranks. I remember one of the veterans posting this last time this happened with someone (I don't remember the guys name but his avatar was constantly changed to a roadsign with a less than polite word on it) so forgive me if I'm mistaken... If you had read them you would have known that. Besides, you weren't the only person who was pranked, I was too, and you don't see me flipping my shit about it.
Calm down jomar, you are overreacting.