Diamonds Are Expensive

You jump up - and bang your head on the lid of the crate and fall down again.
"AGH!" you yell and rub your head. You forgot they nailed down the lids on these crates.
You hear some guards bustling around outside.
"Hey what's that?"
"It came from the crate"
"Man, my back itches. Could you scratch it for me? Ahhh... there. Thanks. What was that you were saying, about a crate?"
You hear the sound of someone trying to wrench open the crate with a crowbar. At least, that's what you think it is. You haven't heard anyone opening a crate with a crowbar recently.
The lid comes flying off. You jump up, and in the process break a guards nose with the top of your head, as he was leaning over the crate to see what was inside.
"FREEZE!" you hear a guard yell. You spin around. He has a Glock 17 pointed at your chest from pretty much point blank range.
You stare him straight in the eye. You're contemplating whether or not he has the guts/ammo to shoot you.
And if he does, how are you gonna get out of this situation?