The ugliest girl in a group of girls that are out. Her friends will not even think of leaving her unless they know she is getting action herself. Therefore, someone in your group of friends sacrifies himself by hooking up with the grenade in order for the rest to have a chance of having sex with the hot girls. More often than not, the grenade jumper gets laid and the rest end up jacking off.
It is good and honorable to jump on the grenade in order to save the platoon. Plus, you will probably get laid while the rest will not.