That's definitely a toughy! I could see that going down alot of ways, some better than others. These are just ways it COULD go down, not what i would do!!!

He's drunk. Reach over, take it from him than proceed to shove it up his ass! Sideways... Thats the reaction alot of up would have, but definately not a smart one... Unless you KNOW you have the upper hand, and have some sort of super secret squirrel training/great luck!

You could ignore him as best as possible, walk out to your car, get your piece out and to a ready in case he comes out blasting, and call the cops, wait for his dumb ass to try anything then either be a good witness or try and play "hero". Either way, you have a pretty good chance of getting shot in the back as you walk away from him... Pretty risky... best option, and just dont give him your back!

You could draw down on him in the store, prone his dumb ass out, and get the cops there... But who knows if his buddies have heat too... And you making a fast motion for a draw may startle him. He already has his shirt up, so he draws and waxes you first... either way, thats going to be an interesting one to see on the cameras, possibly making it harder to defend... especially if the cam doesnt see him brandishing on you, or the clerk doesnt see anything.

Or you could do it croc dundee style and just show him up (you call that a knife...?) by drawing your S&W .500 bear repellent. ok... this is just getting goofy...

GREAT question!!!!! Would love to hear some answers!!!