This reminds me of a couple of Einsteins some years back who pulled the same prank. The difference was they were commercial pilots for a small branch airline and they waterbombed the tower at the San Luis Obispo (CA) airport. Needless to say they're no longer employed as pilots and we're all the safer for it.
I've flown into SBP a number of times - either $100 hamburger runs from Watsonville, or pit stops on my way to LA la land - and found the tower controllers there to be some of least courteous of all the fields I've flown into. Not bad, just not very friendly. Maybe they just pissed these guys off.