A marker most commonly used to indicate where you should not be standing
rather dashing Englishman: Oh My! there appears to be a frag grenade at my feet!
Quite a proper sort of chap: Well it is rather a good job someone put that there or you wouldn't have known where you should not be standing is it not
The act of opening up your hand while your fist is inside of either an asshole or a vagina.
man i totally frag grenaded that chick's ass last night