Triple H and Steph -- Refuse to Work Out With Vince ... 'He's Too Crazy!' (VIDEO)

Vince McMahon is such a BEAST in the gym, even his own musclebound son-in-law refuses to hit the weights with the guy ... telling TMZ Sports, "He's too crazy."

We got Triple H and his wife Steph McMahon out in NYC -- and we asked 'em about their famous midnight workouts ... and how the hell they muster up the energy to train that late at night!!

That's when we brought up 70-year-old Vince -- who's legendary for crushing it in the gym -- and Triple H told us the rumors are true ... the guy is an absolute "machine."

We also got Vince's wife Linda McMahon who told us Vince pumps iron at least 5 days a week ... and when stacked up against HHH and his son Shane ... "He would put 'em all to shame!"

#BEAST