system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do I get the uncontrollable urge to slap my knee or hit nearby object when I'm laughing really really hard?

It's only when I'm in a fit of stomach-hurting-nearly-pissing-myself-laughter. Why does it happen?
gpt
Probably because is a learned behavior you picked up on as a kid. You saw your parents or other adults doing it. And like most kids wanting to be like their parents, or someone they admire, you likely copied them. Over time, it became a part of who you are. 

Source: some dude who does the same exact random little things as an adult that his father does.