Okay, maybe too long and involved if you're really high, but this is a good one.
A man enters a bar with a backpack. He sits down and says to the bartender,
"If I show you something you've never seen before, can I have a free drink?"
The Bartender replies,
"It better be amazing, because I don't surprise easy."
The man reaches into his bag and pulls out a tiny bench, piano, and a 12 inch tall man in a tuxedo. The little man sits at the piano and begins to play music.
Everyone in the bar shouts with excitement, and the bartender gives the man his free beer.
After the bar quiets down again, the bartender asks
"Where did you find this man?"
The mysterious backpacker replies
"It all started when I found this lamp"
He then takes out a golden lamp from his backpack. The Bartender quickly snatches the lamp away, rubs it, and a genie appears.
The bartender shouts all at once
"I wish for a million bucks!"
Suddenly the bar is filled with ducks, and everyone is either forced to the ground or pushed against the walls.
In the ensuing chaos the backpacker and the bartender manage to escape the bar. Panting and bewildered, the bartender says to the man
"I said bucks, not ducks!"
Recovering himself, the backpacker looks at the bartender, and shouts in disdain
"What did you think I wished for, a 12 inch pianist?!"