You're so skinny, you can barely fit through a door crack.
Skinny Door Crack
Explanation
Explain Bear
Listen up, buttercup. This joke is all about how super-duper skinny you are. Like, so skinny you could slip through the tiniest gap in a door. And you know about doors, right? Those things that keep the wind out and your terrible jokes in. I'm just messing with you, I love your jokes!