You have strong arms, so you thought it would be a good idea to challenge your bully to show your gf what a man you are. You were wrong. Your bully knew what he was doing. You paid a high price for your loss.
Gave them the Goldenballs scenario: They can either split the punishment evenly. Or try to get one of them to endure the whole punishment. But if both pick that, they both endure it for double the time.