When a girl is deepthroating you, you slap her after she spits out a lot of flem. This comes in handy when the girl bites your dick so you just slap them to make them not to it as often. Slapping them gently makes them laugh and also builds up more spit.
I was deepthroating but my cock on her face then I slapped her gently. This gathered more spit from her mouth which made deepthroating more interesting. This is called a slap happy deepthroat!