Fnoop
A Fnoop is when you flatten out your hand like a high 5 but hold your hand palm-side up and charge it into someone's stomach when they're not expecting it.
"I saw Darla a little while ago and she fnooped me. I still have the feeling on my stomach"
"Aw that sucks, I hate getting fnooped, it hurts."
"Aw that sucks, I hate getting fnooped, it hurts."