Who said it first if you cant beat them join them?

These proverbs mean "If you can't stop someone from doing something, then go ahead and do the same thing as them."

Pretend there is a law that says people must not wash their cars. But everyone ignores this law, and washes their cars every day. You obey the law, but you are the only one driving a dirty car. You complain to the police, but they say they don't care. After months of complaining and driving the only dirty car, you decide to join everyone else in breaking the law, and you wash your car.If you can't beat them, join them.

The Yale Book of Modern Proverbs will cite the following as its earliest example:

1902 Des Moines Homestead 13 Feb: "The father-in-law said, 'If you can't beat them, join them.' And I believe tonight if I can't beat the Short-horn association I will join them."