Dana White says he could "give a s**t" if MMA fans bail on UFC over his friendship with President Trump ... telling TMZ Sports, "That's your problem, not mine."

Just last week, the UFC boss flew with POTUS to Colorado for a campaign rally -- where White even took the mic and fired up the crowd before Trump spoke.

When we saw White outside of Mulberry Street pizza in Bev Hills on Thursday, he told us how the whole thing came together.

"I wasn't really campaigning, he called me and asked me if I wanted to go to Colorado," White said ... "he said, 'Wanna go to Colorado?' So, I said, 'Yeah.' So, we flew over to Colorado for the day and then back to Vegas."

So, what did they talk about on Air Force One?

"We were just hanging out and talking fights."

"I can't say it enough. This guy, when I say this guy I'm talking about President Trump ... is such a good friend and such a loyal amazing guy. He's a great guy, been a friend of mine for a long time."

As for backlash from UFC fans upset with White for supporting Trump, Dana made it clear he doesn't care if the friendship rubs people the wrong way.

"I could give a s**t. I don't give a s**t. If you don't like me because I'm friends with this guy, that's your problem, not mine."

There's more ... Dana is also very close friends with Tom Brady -- so we asked White if he knows anything about where TB12 could end up next season?!