Reserve Inch

When you're having sex with a girl for the first time, don't insert your penis all the way in, leave at least an inch outside the vagina. So in the case that the girl asks you to "go deeper" you have some dick left to give her.

She's asked me to go deeper, lucky I still had my reserve inch. Phew!

I forgot to leave a reserve inch, when she asked me to go deeper I couldn't and she laughed in my face.