Another way of telling someone to shut up or shush.
David: "So, did you score? Did she kiss you? Did you get her number? What did she smell like? Are you gonna go out with her again? Do you think this is true love?"
Jonathan: "David.. SHISH KEBAB!!!"
The shish kebab is a dish of small cubes of meat pierced and held in place on a skewer. Using this term as a reference to the act of love adds an exotic twist (brings up images of the middle east were shishkebabs were invented) to the already blunt metaphore of the skewer penetrating the meat.
"Have you shish kebabed her yet"