When the woman got to the counter, Prusak politely asked her to return the money to the young man who dropped it, and she refused, claiming it was hers.
Prusak said again that the money was not hers, and after going back and forth with the woman, said, "Please return the $20 or get out of the store, because I'm not going to serve someone as disrespectful as you."
The woman left the store without returning the money, after yelling and swearing at 19-year-old Prusak.
Then Prusak took $20 out of his own wallet and gave it to the blind man "on behalf of Dairy Queen" and apologized for the incident.
One customer who witnessed the incident wrote a lengthy email to Dairy Queen in praise of Prusak, saying she "never would have expected" such an act of kindness.
"I was in shock by the generosity that your employee had," the customer wrote. "I would proudly like to say that Joey has forever sealed my fate as a life long customer of [Dairy Queen]. Thank you for outstanding customer service and for an even better experience."
The email went viral after being shared online, and now the store has seen its traffic double, and customers have been calling the store to thank Prusak and even offer him jobs.
Prusak, who says he just did what most people would have done in that situation, has been working at the Dairy Queen since he was 14 saving up money to go to business school. He has been manager of the store since earlier this year.
Even billionaire Warren Buffet, whose company owns Dairy Queen, called Prusak and thanked him for being a role model to other employees. International Dairy Queen is now figuring out how to reward Prusak for his good deed.