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.
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.