Either it's a prank or somebody has a crush on you and is not out of the closet yet.
Are you into it? Make sure it's not a prank, then go for it. If not, assume it's like a woman you don't like is interested. Have a short talk about it, make sure he understands you are not interested and be direct but not cruel about it. Don't out him, be respectful about his feelings. Adults do that all the time. The first time is just a little scary, but you will learn to handle that with routine soon.