CM Punk says he's not worried about embarrassing himself during his UFC debut ... because he once crapped himself during a WWE match ... so, how much worse could it be??
The 37-year-old is gearing up for his MMA debut at UFC 203 on Sept. 10th ... and was asked if he's nervous.
"It's funny because you can ask yourself, 'What happens if I lose? What happens if I get embarrassed in front of the world?'"
"And then you think to yourself, 'Well, you s**t yourself on national television before so how bad can it go? How bad could it really be?'"
FYI, the incident Punk's talking about went down in 2013 -- when Punk gave WWE fans a little more than they bargained for during a bout with Dean Ambrose.
Hey, at least he won the match ...