The only thing you should put in your anus is your elbow.

No, wait, that's ears.

The only thing you should put in your anus is your ear.

No, no, that's still not right.

The only think you should put in your anus is something with a flared base.*

*If you're worrying about whether your boyfriend's penis has a flared base and you can't find a tape measure, recall that most penises are not readily detachable, and most boyfriends have hips wider than their penis, so you're in the clear.

If you're worried that this advice doesn't apply simply because you don't have a boyfriend, there's an app for that.