The owner looks at the TV set, then looks at the stoner, and says, "I don't sell stuff to potheads." So the stoner tells the owner that he'll quit toking and will come back the next week to buy the TV. A week later, the stoner comes back and says, "I quit smoking pot. Now, how much for that TV set in the window?"
And the owner says, "I told you I don't sell to potheads!" So the stoner leaves again.
He comes back a week later and says, "How much for that TV?"
The owner says, "I'm not going to tell you again, I don't sell to potheads!!!"
The stoner looks back at the owner and says, "How can you tell I'm a pothead?"
The owner looks back and says, "Because that's a microwave."