Because if you want me to "act professional", I can tell you that I'm not interested. I'm sitting in my home office wearing a bathrobe. The same way I'm not going to start wearing ties, I'm *also* not going to buy into the fake politeness, the lying, the office politics and backstabbing, the passive aggressiveness, and the buzzwords. Because THAT is what "acting professionally" results in: people resort to all kinds of really nasty things because they are forced to act out their normal urges in unnatural ways.
-- Linus, on the kernel mailing list, 7/16/2013, on why he will continue to cuss out folks