chiming in... it does not seem that the photographer has or intended to use the photo of the bike (key word), that happens to have been painted, for commercial use. either way if taking a photo of the paint on the bike is copyright infringement then taking a photo of the bike itself would be too. i dont see how it would be though since the owner of the bike paid for the bike and paid for the paint job. the paint job itself is most likely a commissioned job and if custom the bike owner would assume he owns it. i doubt in either case that the owner of the bike signed a copyright restriction for either. thus he should be able to have a friend take a photo of "his" property and do with it what he wants whether he paid this friend or not. even if he made a million bucks off showing the bike the painter has no right to that money.
that said, the photographer owns the photo. now if he gave it to his friend and his friend gave it to someone and somewhere down the line the painter ended up with the photo the photographer is SOL. he should have given the photo to his friend with certain use restrictions. if the painter stole the photo off his site then that is copyright infringement. the thing to clear up is how the painter came to have possesion of the photo file?
and generally speaking, if i saw a shirt that said xxx photography sucks i would probably go check out their site. if your work sucks i would laugh and go about my day. if it is good, however, i would probably think it was a publicity stunt. either way i went to your site and made my own decision.
the lesson is: some people suck, and people like this only get worse the more you respond. just leave it alone unless they do physical or severe character harm.