I think it is situational of course. Wearing concert T shirt to a concert? That makes sense, though they still are not very flattering. I personally wouldn't wear them as I see them as sloppy and unkept. I collect concert shirts but don't actually wear them. I wouldn't really want to be out with a guy around town wearing them, as I view concert T shirts in the same category as sweatpants, pajamas, tank tops or other items that I would not consider to be something one should wear in public. A guy running around in concert shirts is kind of like how many view a girl running around in hair rollers or a face mask, it is not very presentable or attractive.