The phrase used when someone does something that most people don't agree with; socially unacceptable; politically incorrect.
This phrase cannot be used in reference to dill
pickles, because I'm pretty sure those are
always kosher.
Jack:
John, are you stealing those little kids' lunch money again? You're like 40 man you need to stop that.
John: (Looks down at his feet with shame)
Jack: Not kosher man, not kosher at all