Who uses it: Military personnel, particularly infantry
What it means: Assassination of an officer by his own troops, especially with a grenade ("frag" is military slang for a grenade, because it fragments on detonation).
How you can use it: When taking aim at a superior.
It was just a matter of time before the Vice President ran amok with a gun in his hands. Really, didn't we all see it coming? I guess we should all just be grateful that it happened on a remote Texas ranch, and that the person who got in his way was a 78-year-old man and not a 30-something mother of three.
No one could make this stuff up, and I can't say anything that would make this more horrifying or hilarious than it is.
Today is my brother James' 30th birthday, so love and best wishes to him as he starts his fourth decade. Happy birthday; no matter how old you get, you'll always be the baby of the family.
Update -- My cousin Sheila has weighed in on Mr. Cheney's accident, in her own inimitable way. Check it out here.