This guy's first mistake was failing to come up with a FAKE excuse for skipping work.  But it wasn't his biggest mistake . . .

20-year-old Kentarias Gowans was supposed to work a Thanksgiving Day shift at a Steak 'n Shake in Oakwood, Georgia.  (About 50 miles northeast of Atlanta.)

But he called in and said he couldn't work, because he was too DRUNK to make it in.

It's not clear how his manager reacted to that.  But Kentarias DID end up showing up later that night . . . to ROB the place.

He was still drunk around 10:00 P.M. when he walked in with a GUN . . . held it to a co-worker's head . . . and demanded money.

Multiple people called 911, and cops happened to be in the area.  So they got there in under a minute, and saw people running from the building.

When they ordered him to drop the gun, he RAISED it at them for a second, but they didn't shoot.  Then he did finally drop it.

He's facing multiple charges for aggravated assault, having a concealed weapon without a license, underage drinking, and public drunkenness. 

(Gainesville Times / AP)

(Here's his mugshot.)