When Joey Prusak saw an old lady steal $20 from a blind man, he did what he thought was right. The 19-year-old Dairy Queen employee refused to serve her.

Prusak, who was working the cash register at a Dairy Queen store in Hopkins, Minn., on Sept. 10, was serving one of his regular customers, who is visually impaired. When the man was checking his pockets for money, he dropped a bill on the floor.

"Right then and there I knew when he dropped that $20 bill, game's over, he's not going to know," Prusak told KARE. "He just kept walking and that's when the lady picked it up and I thought, she's going to give it back 'cause she picked it up so quickly."

But the lady put the money in her purse and then approached the counter to place her order. At first, Prusak did not know what to say, but when he confronted her about the cash and she refused to return it, Prusak asked her to leave.

"I said, 'Ma'am, I'm not going to serve someone as disrespectful as you, so you can either return the $20 bill and I'll serve you, or you can leave,'" Prusak said. "And she goes, 'Well, it's my $20 bill,' and I go, well then you can leave."

Among some customers who witnessed the interaction, one in particular later saw Prusak approach the blind customer and hand him a $20 bill out of his own pocket.

Dairy Queen
A letter written by a Dairy Queen customer describing Joey Prusak 's altruistic actions. Reddit

“I would like to give you the $20 you happened to drop on the ground as you walked away from the counter. I realize it is not the $20 bill you dropped because the older woman stole it, but it does have the same face value,” Prusak reportedly said.

The passerby wrote down what he saw and submitted a letter to Dairy Queen, where it made its way onto the store’s bulletin board and eventually onto Reddit and Facebook, where it has since gone viral.

“People started sharing it and liking it,” Prusak told CBS Minnesota. “And one of my friends saw it and posted it on reddit.com. By Monday morning it was one of the top things.”

The anonymous letter ended by saying, “Joey has forever sealed my fate as a lifelong customer.”

Prusak insisted he acted out of moral imperative. “I felt like the right thing to do was to give him the money,” he said.