The solitary ugly girl always found with a group of hotties. If the grenade doesn't get any action, then neither does anyone else.

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

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.

A group of ugly, fat, pale, repulsive, and/or slovenly females.

The term "grenade" was coined by The Situation on MTV's infamous show, The Jersey Shore

Hand- held explosive, used mainly by people who wish to inflict pain and death. (eg. Terrorists, soldiers)
To use a grenade, one would remove the pin and throw the grenade in the direction of the target, where under normal circumstances, it would explode.
Not reccomended for children. Or anyone at all, really.

Similar to a timebomb, a roach with weed packed on top

an ugly girl that is jumped on for the sake of your friends. Similar to the times of war when the enemy tosses a grenade over the lines and a comrade jumps on it to ensure teh safety of others.