The Australian took the bet one step further asking his boss to change his hairstyle into a mohawk.
Brown appeared to live up to the bet in the McLaren garage at the Belgian GP, however it was not what Piastri originally meant.
The 52-year-old copped out of the bet by wearing a bald cap with an orange mohawk on it, failing to deliver on his promise to his winning driver.
Piastri nearly made it a second consecutive win at Spa, beating his team-mate at the start to get ahead, and was closing in on both Mercedes towards the end of the race.