Because it's not allowed.
Because it's not good for you.
Because your eyes will stay that way.
Because we didn't have that luxury in my day.
Because it isn't fair to the rest.
Because no one's ever done it.
Because it's too hard or too easy.
Because once you do it you won't want to stop.
Because in all likelihood you'll find it isn't what you'd imagined it to be, but by then it will be too late to undo it.
Because it's uncouth or uncool or it shows bad breeding, or too much in-breeding, or it's not being clever. In any case, it's just not done.
Because 'Y' is a crooked letter.
Go ask your mother, or conversely, go ask your father. If s/he says it's all right, then it's all right with me.
You'll understand when you're older.
Because you're not a kid anymore.
You just shouldn't.
No, really, you should.
I don't see why not.
