Brown spoke with reporters on Thursday about his now-infamous tweet ... saying he "obviously" doesn't actually want to leave the Steelers after clapping back at a tweet suggesting Ben Roethlisberger is responsible for his success.

AB84 explained he fired back at the guy who sent the tweet -- a former Steelers PR guy -- because he thought it was a personal shot.

"I'm still grateful to put on my uniform, grateful to be a part of this organization," Brown said. "I don't take that for granted. Obviously it was a stupid remark."

Brown also said he's pissed the Steelers haven't won a game yet ... but wouldn't reveal why he missed practice on Monday.