9:20 AM PT -- Dave Coulier responded to the John Stamos haters this morning on his Instagram.

"I'm sorry to see a bunch of negative comments as I've just begun my cancer journey.

"It's our friendship (me and John) and this is how we are handling a very tough time. I'm a comedian and humor is what drives me. John knows how to cheer me up and I laughed out loud when he arrived wearing a bald cap - being a true and loving friend and brother."

John Stamos is showing solidarity with his friend and former TV castmate Dave Coulier during his battle with an aggressive cancer, but some people online are taking issue with his method ... calling him insufficiently committed to the cause.

Stamos posted a few pics on Instagram of fellow "Full House" actor Coulier, featuring Stamos wearing a bald cap and shaving Coulier's head, who's going through chemotherapy treatment after his recent cancer diagnosis.

Coulier is battling stage 3 non-Hodgkin lymphoma, an aggressive form of cancer. The pic shows Stamos shaving Coulier's head, and the friends are both smiling ... as Stamos acknowledges he used a little Photoshop magic to make the bald wig blend. A third shot shows Dave's wife, Melissa, and John both kissing Dave's freshly shaved dome.

But, because no good deed goes unpunished, online trolls are taking offense and calling out Stamos for being "shallow."

Several commenters took issue with Stamos' decision to wear a bald cap. Some seemed to suggest putting on a bald cap was not much of a commitment to his friend. "Seriously just couldn't shave your head bro?" said one.

"I can’t help but feel that you’re using Dave’s diagnoses as a way to make yourself more likeable,” said another commenter, with yet another noting "You made sure to post it on Instagram to get those likes too."

Others were in favor of Stamos showing his support, calling it inspiring -- "If Dave isn’t offended by this, you shouldn’t be either ☺️and remember … John is an actor and may need his hair for his JOB."

Coulier announced his diagnosis just last week, and has already begun treatment. Stamos and Coulier, both in their 60s, worked together on the fan-favorite family show "Full House" back in the 1990s -- fellow star Bob Saget died in 2022 from a head injury. They all worked together on the show's reboot, "Fuller House."

Coulier said he's been told he's in the 90-percent "curable" range -- and he sure does appear to appreciate John's gesture. Trolls take note!