CM Punk -- Laughs Off Green Ranger Challenge ... For UFC Debut

CM Punk could choose ANY opponent for his UFC debut ... but it almost certainly won't be the Green Power Ranger -- not based on CM's reaction to the guy's name, anyway.

The former WWE champ was in NYC Thursday when he told our photog how training is going for his first bout in the Octagon. His new UFC contract was announced earlier this month.

CM wouldn't name names yet as far as his first opponent -- looks like he's enjoying the speculation. But you gotta see his reaction when we bring up Jason David Frank -- a former Power Ranger who's been calling out Punk. He's clearly not impressed.

Go go ... go to sleep.