In an AU where Clark didn't have a wholesome upbringing, or maybe something went very wrong when he moved to the big smoke, his secret identity isn't as wholesome as a reporter. Perhaps he's a rent boy, or a private bodyguard, or just a trophy boyfriend by some rich playboy (Lex, perhaps?).

But he's still Superman, and that's how he justifies his less than legitimate day job.

Except now he's involved with Batman and he can't bear to let Bats know who he is without the cape.

Would love Clark being very ashamed and Batman (being Batman) finding out the truth and accepting him.

Bonus points for Bruce Wayne and Clark Kent meeting under unsavory circumstances while they're both unaware of who the other it.