3:58 PM PT -- Shaun White has pulled the photo of his "Simple Jack" costume off of his social and has issued an apology.

"I owe everyone in the Special Olympics community an apology for my poor choice of Halloween costume the other night."

"It was a last minute decision. It was the wrong one." White says.

"The Special Olympics were right to call me out on it. They do great work supporting so many tremendous athletes and I am sorry for being insensitive. Lesson learned."

Shaun White is under fire from special needs parents AND the Special Olympics over his Halloween costume -- Simple Jack from "Tropic Thunder."

Remember, when the movie came out back in 2008, several disabilities groups blasted Ben Stiller and the flick for the character -- an intellectually disabled man who is repeatedly referred to as the r-word.

Now, 10 years later ... White thought it would be a good idea to trot out the costume for a Halloween party and people are pissed.

In fact, a rep for the Special Olympics tells TMZ Sports ...

"We are truly disappointed that Shaun White, an acclaimed Olympian, would choose this costume which is so offensive and causes so much pain."

"Disability is not a joke nor should it be a punchline. We hope that Shaun White and others learn that this just continues stigma, stereotypes and discrimination."

Others have sounded off on Shaun's IG page -- where he posted the pic.

"I'm not sure if it’s worse that this is an actual movie or that you’d think it’s okay to mock individuals who have disabilities. It’s 2018, man. #spreadthewordtoendtheword #rwordhurts," one person wrote.

Another wrote, "You’re a real POS! Really? At the expense of those who can’t defend themselves?? Hope you’re working on your lame apology speech...I know this will be deleted!! Grow up you douche! #spreadthewordtoendtheword #specialolympics."

We reached out to White's agent for comment -- so far, no word back.

Originally published -- 9:20 AM PDT