The act of sexually penetrating someone without a form of contraceptive, such as a condom.
Matt: Dude! Jay, I can't believe you raw dogged brooks' mom last night!
Tummy sticks is the situation, commonly referred to as a game, in which two erect men cuddle closely and face-to-face causing their two erect penises, or sticks, to push upwards between their stomachs, or tummys. Sticks combine with tummys, hence the name "tummy sticks."
Adam: "Hey Brooks, instead of going fishing let's stay home and play tummy sticks!"