This sounds like a bartender where I used to live - Fred (names changed) was just a complete asshole to everyone, all the time. My buddy Jay (who can be a world-class asshole himself, at times) went in one afternoon and got sweet revenge - petty, childish and stupid revenge, but sweet nonetheless, as those adjectives all described Fred as well. Note the building was only about 20 feet wide, but probably 100 feet deep, and the bartop itself is very long, so Fred did a lot of walking in the following story.

Jay walked in, no other customers in the building. Fred was seated at the end of the long bar watching baseball. Jay took a seat at the far end. Eventually Fred got up, came down and said "What do you want?" (He's a real charmer, our Freddie.) Jay ordered a small pitcher of a beer whose only tap is at the other end by the TV. Fred pulled the pitcher, brought it down, and said"$4.95". Jay gave him a $5... Fred rang it in... and returned to his seat in front of the TV.

After a minute, Jay called down,

Jay: "Hey, Fred? Where's my change?"
Fred: "It's only a f*cking nickel!"
Jay: "I know, but it's my f*cking nickel, so how about you bring me my change?"

Fred got up, got the nickel, stomped down to Jay, slammed it down on the bar and said (again, I kid you not) "there's your f*cking change, happy now?" And stomped back down to his seat again.

Jay smiled and said thank you... then picked up his beer and moved to a seat at the near end of the bar to watch baseball.