Sorry...was editing my post...after yours.... Its the gas station thing...need collateral to get the key back....UA BP won't work because they cant type in the system deny boarding because you refused to give back the key to the shower room...Something else instead will work...(ID, membership card, Passport)

Another option if you only want to do the BP as collateral for the shower is book a refundable ticket, print BP, use BP for the shower collateral, take shower, then cancel ticket.....