Basically when you've got diahhrea. It's a combination of a number 1 and a number 2. So when you piss out of your ass you can politely refer to it as a number 3.

a condom full of jizz

To go both number 1 and number 2 at the same time
Both pee and poop

When you go to the bathroom to pleasure yourself. You're not going number 1 or number 2.

jagging off, masturbating, choking the chicken, etc. etc.

Having diahrrea or the action of urinating and passing a bowel movement at the same time.

The guy you’re supposed to end up with. Refer to ep. 88 of Call Her Daddy.