Ha ha, I’m stab susp!

A MANHATTAN straphanger was stabbed in the gut by a knife-wielding maniac despite clocking the attacker in the head with his cane early Saturday, cops said.

The early morning underground mayhem started when James Purnell pulled a knife on a 28-year-old man as the downtown C train left the 125th St. station around 6 a.m., police said.

Purnell bolted with the victim’s knapsack and cell phone before targeting a second rider only a few minutes later.

Nick DiRenzo, 62, refused to surrender his belongings when threatened by Purnell, police said. DiRenzo fought off the 39-year-old lunatic by clocking him in the noggin with his cane.

But DiRenzo’s efforts couldn’t stop Purnell from stabbing the Washington Heights man three times, causing internal bleeding, police said.

Purnell ditched his blade and tried to create a diversion when cops finally busted him at the 59th St. station.

The suspect, sporting a wide grin, emerged hours later from a transit police station with a cut over his left eyebrow and his feet shackled.

Purnell’s rap sheet dates back 22 years and includes 25 arrests, beginning with a 1995 bust for menacing and finishing with a 2015 arrest for petty larceny.

He was remanded to jail after his arraignment in Manhattan Criminal Court Saturday night.

DiRenzo was taken to Mount Sinai St. Luke’s Hospital, where he underwent surgery.

“He’s doing good,” a relative said at the hospital.

James Purnell looks like he couldn’t be happier about being arrested Saturday after he allegedly pulled a knife on a man who then bashed him in the head with a cane.