What do you do when a cute girl shows off her t-shirt to you?

Ok, so if a cute girl your with has an awesome t-shirt (i.e thundercats/batman logo) and says, "yeah isn't my t-shirt cool!" then turns and faces you so you can get a good look at it, I always feel awkward about it. What should I do in these situations?: take a look and feign a, "I'm genuinely looking at your shirt and not at your boobs." face?