a female actually slapping someone on the face with their fanny. Usually the victim has to be laid down unless the female is particularly versatile.
James: Damn! last night i thought i was gonna get some
Kelvin: oh yeah? what happened?
James: She threw me on the bed but then just gave me a massive fanny slap!
When you physically slap someones fanny, as a punishment for a bad blow-job.
girl, that blowjob was sooooo shit your gonna get a right fanny slapping!
A fanny slap is a slap that sounds like when you slap a fanny, it usually associates with a ruler and slapping it on the table anything that makes that tingling sound is known as a fanny slap. Could even be a spatular.
Person 1 & 2 are in the maths room
*Person 1 slaps his ruler across the table*
Person 2: Did you hear that?
Person 1: Yer it sounded like a fanny slap!