Turn down free money to punish an unfair split? Most people do exactly that.
In Werner Guth's 1982 ultimatum game, one player proposes how to split a sum of money and the other can accept or reject it — rejecting means both walk away with nothing. A purely self-interested responder should accept any offer above zero, but most people reject offers below roughly 20-30% of the pot, giving up their own payout just to punish an unfair split. The result has held up across decades of replications in dozens of countries.