Inside inside joke

Simply put, an inside joke with yourself. If you have to many of these, it is no longer a joke, its a mental condition.

Me: I was just climbing the tree and...

Classmate: HAHAHAHA!!!!!!

Me: Uhhh, dude, I haven't even got to the marginally funny part. What's the big deal?

Classmate: Oh nothing, just thought of something.

Me: Care to share?

Classmate: No not really, just an inside inside joke.

Me: I'm just going to move on then. So i was climbing the tree...

Classmate:HAHAHAHAHA!!!!!!!

Me: Sigh.