Simple. I do it for my own amusement and to piss off the right sort of people who are guaranteed to over react when I tell them about it and give me smiles.
Honestly though, just between you and me, I'm against boycotts. If those who get angry hearing mentions of my personal boycotts (which incidentally includes movies at the theatre and I break that one at least once a year) really wanted to shut me up all they'd have to do is join them.