The Curse of Hooligan's Bar by Charles E. Fritch

The narrator sits alone at Hooligan's bar on New Year's Eve and orders Martinis. Hooligan gives him a martini "on the house," so he doesn't complain about the drink missing an olive. When the clock strikes twelve and the celebration begins around him, the narrator spots a tiny leprechaun vampire emerge form the cuckoo clock. The narrator, down on his luck, strikes a deal with the his new friend where they will both make it in showbiz. As he goes to tell Hooligan, the bartender stabs the tiny vampire through the heart with a toothpick, thinking he was an olive with his red hair and green get-up.

Pretty good little story. Reads like a long joke with a pretty good punch line at the end.