Prematurely laughing

When you laugh way too early at something or before anything has even happened.

“Why are you laughing?”

“Im prematurely laughing really funny movie part coming up”

Blackout laughter

Much like blackout drunk, but you laugh so hard you can’t remember what your even laughing about.

I was going to tell my friend about this hilarious joke but I had a case of blackout laughter and couldn’t remember what it was