For Luke Bryan, things getting thrown up on stage or near him is probably something he's used to at this point in his career. And naturally, when someone throws something at you, you're going to catch it out of reflex. Especially if you don't know what it is.
Bryan was performing at a show and when a fan threw up underwear on the stage. Bryan caught it and threw his hands in the air, then he realized what he was holding. He quickly tossed it to the side and kept performing... all while laughing at the whole situation.