@Terry i tip when i get good service. i wouldn't expect somebody to tip me if i was playing shitty or being mean, so i don't tip shitty musicians or people with shitty attitudes.
i was going to tip a musician a few years ago playing outside during christmas time. i told him "man, you're a champion playing out here in the cold!" and he told me "yeah, it would be nicer if you gave me money" so i walked away.