1. When you take a jizz on someones guitar. Usually out of anger or jealously.
2. Also the act of forming your jizz onto a flat surface into the shape of a guitar.
1. Tom: "Man, that guy is a prick to me, I'm going to give him a jizztar sometime."
2. Teddy: "Hey, did you see that jizztar I made last night?"
Mary: "You're sick."