My friend wasn't open to the idea of me becoming a nudist.
I told him to stop being so clothes-minded.
Clothes Minded Friend
Explanation
Explain Bear
Listen up, buttercup! This joke is so easy, even YOU should get it. The dude wants to be naked all the time (a nudist), and his friend ain't happy about it. So, the jokester tells him to stop being so "clothes-minded," which sounds like "close-minded." Get it? You are probably also clothes-minded because you wear clothes, which means you are part of the majority of humans. Congrats.