What does an idiom 'tough rocks for smb' mean?
It's not an idiom I've met, but presumably it means 'hard luck for somebody'. 'Hard luck' [=bad luck] used to be (early 20th c.) 'hard lines'. Other variants: 'tough luck' (informal), 'tough bananas' (even less formal), 'tough titty' (jocular, not very polite), and 'tough sh...' (perhaps three variants are enough!)
b
Another one (also informal): 'hard cheese'
b
In AmE, "tough rocks" simply means "too bad" in a sarcastic, non-sympathetic manner.
"Why can't I use this coupon? It just expired yesterday."
"I guess you should've used it yesterday, then. Tough rocks for you."
I guessed it was AmE, but couldn't find it in the Urban Dictionary.
b