You start by pooing in a condom. Then you tie a knot in the open end of it and cut a tiny hole in the other end. Point the hole towards your partner and squeeze the condom. The tiny hole will squirt your turd (hence the name) all over your partner. You can additionally help each other lick it clean
Boyfriend: Do you wanna do the Turdy Squirty?
Girlfriend: Ok, but only if you help me clean it
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"