jack party - A party where people all jerk off, and some of them even do

A party where people all jerk off, and some of them even do it together like they're in a group and not just alone.

This jack party is just a bunch of people jerking off, and some of them are doing it together.

I came to the party and it turned into a full-on group jerk off.

This is the best jack party I've ever been to, and I'm just jerking off with everyone.