The cowardly thug who killed actress Nicole Dufresne isn’t entitled to a new trial, an appeals court ruled yesterday.

Rudy Fleming, who’s currently serving a life sentence for Dufresne’s 2005 murder, says he was diagnosed in prison as psychotic and wants a hearing to show he was too far gone to be held responsible for the killing.

The state Appellate Division panel noted that Fleming had psychiatric exams both before and after the trial, where psychiatric experts concluded his claims — including that a giant marshmallow man had visited him in his cell — were at best “grossly exaggerated.”