“Did you just trip the goddamn alarm?”  Why did he keep working with Joker?  No, really, why?  It never ended well for anyone involved.  He’d leave Croc for the cops or the Bat, Croc’d put him in a body cast for a few months…  it always ended in one of them getting fucked over.

And here they were, in a real classy jewelry store, with Joker deliberately setting the alarm off.  

Once again – why?    

Maybe Croc was a closet masochist.