We can't all be rock stars, but no matter what line of business you're in, plagiarism is plagiarism.  Let's say you're a welder, wouldn't you be a little annoyed if someone copied your weld and made the signature look almost exactly like yours, but scored cash off your knock-off?  Not sure if Duff was just curious, annoyed, entertained, or angry, but he explains being kicked out of a store full of bootleg merch in Japan in his Seattle Weekly blog.  You can read it here.