John Stamos Responds to Comments About Wearing Bald Cap With Dave Coulier

John Stamos is firing back at critics who slammed him for wearing a bald cap while shaving his buddy Dave Coulier’s head as DC battles an aggressive form of cancer.

We caught up with John at LAX, and he’s not having it, telling us he’s actually embarrassed for the haters ... saying they’re wasting time making hate videos and comments when they could be using that energy to call their doctors and get checked out.

Check out the full video 'cause John’s shock is crystal clear -- especially as he gets real to us about how it's hurt him, explaining he was just trying to cheer up a friend when Coulier asked him over to shave his head.

When it comes to the reason why he didn't shave his own head in solidarity, John’s got a solid reason -- which he explains to us.

In the video, John also makes it crystal clear -- he’s not sorry at all ... going on to describe the night with his "Full House" cast mate and dear friend, a buddy being there for another in a time of need.

Coulier is battling stage 3 non-Hodgkin lymphoma, an aggressive form of cancer -- he announced his diagnosis last week and has already begun treatment.