thumb bowlin'
when you are doin a girl from behind and you stick your thumb in her ass as an anchor. When your ready to nut you pull your thumb out and she farts.
This sound would be like if you were throwing a bowling ball and only use your thumb. When you release the ball it will make a popping sound.
"Last night I went thumb bowlin' with my girl." "Man she really popped!"
"Last night I went thumb bowlin' with my girl." "Man she really popped!"