lol I went to a local music venue a few weeks back and tried this. After inquiring about one guys shirt, he started at me for a few seconds like I was insane and turned around
If someone at a concert acts like you've insulted them by asking about their music related shirt, then the problem is with them, not you.
This is precisely why I don't feel bad about asking innocent questions.
If they can't handle basic conversation, it's them.
Then you have the perfect opener for anyone overhearing by cracking a joke about it.