So I'm 18 years old and very shy, and my mom suggested I go to a Japanese spa to relax.

So I strip down and put on the robe they give you, and as I'm walking into the open area with all the mud baths and hot tubs, one of the workers there said "Oh, let me help you with this", and she yanks on the belt of my robe, pulls it RIGHT off my back and SHOVED me into the open area of people, while slamming the door behind me---leaving me out there BUCK NAKED!!!

I immediately covered my penis with my hands, and I started BEGGING the woman to let me have my robe back.

As I'm bouncing there on my tippytoes, trying to look into the window to get her attention, I hear all the people behind me LAUGHING at my bare misfortune.

Then, the most humiliating thing happened:

A 45 year old woman there gets out of her hot tub, puts on her robe, walks behind me and says "Just get in a tub, SWEET CHEEKS" and SLAPS my naked tush!!!

Why does my friend Sarah think this is SO hilarious???

What mental images are so hilarious to visualize that makes people laugh so hard?