When you laugh so hard, sometimes people say "OMG I"M PEEING." Imaginatively speaking, you pee so much that you are now swimming laps in your piss. Laps is used when something is beyond funny and u can't stop laughing. It could be a substitute for LMAO.
When you are reading a manga/manhwa or watching an anime and something cute or hot happens, then you need to get away from ur phone/pc for a bit to process what just happened, so u run laps (probably around ur house)
Simmons: Just for talking back, you can't do girly laps.
Grif: You've gone blind with imaginary power, Simmons.
Simmons: Oh ho, on the contrary, I think I've gone blind with very real power.
Sister: Seriously, what the fuck are girly laps?!