Keep yourself safe. Don't sign off the pilot, or even train him further unless you get to choose the examiner. That way, when the FAA calls after the pilot violates yet another reg causing an enforcement action, you'll be in the clear.
Heyas,
I agree with Jedi. Distance yourself from this situation ASAP. From the sounds of it, it seems like the student/instructor relationship is pretty well poisoned, so I'd recommend that he seeks instruction elsewhere.
If you HAVE signed the guy off, void those endorsements as soon as you can.
If the guy's performance is SO horrible that you fear for someone's safety, then seek out the local FAA ASR and express your concern to them. They may or may not "flag" him, but you will have washed your hands of the situation.
If you have a student that is weak, but is willing to try, try, try and to spend, spend, spend, to get up to speed, that's one thing, and those are the kind of people you help.
OTOH, if you have a weak student that is just looking to short the system and slide through hoping the autopilot will save their tail in the soup, then that's the kind of situation you want to exit.
Nu