what does "keep his butler in fucking bath salt"mean?
“Mr. Strike, your attitude astounds me. You undertook to repay Mr. Rokeby monthly, and you are now in arrears to the tune of—”
“I can’t pay you what I haven’t got. If you hold tight, I should be able to give you all of it back. Maybe even in a oner.”
“I’m afraid that simply isn’t good enough. Unless you bring these repayments up to date—”
“Gillespie,” said Strike, his eyes on the bright sky beyond the window, “we both know old Jonny isn’t going to sue his one-legged war-hero son for repayment of a loan that wouldn’t keep his butler in fucking bath salts. I’ll give him back his money, with interest, within the next couple of months, and he can stick it up his arse and set fire to it, if he likes. Tell him that, from me, and now get off my fucking back.”