Richard Jefferson has big beef with a former NBA ball boy ... admitting he was a jerk to the guy, but explained it's all 'cause the man used to stare at his "junk" in the locker room.
Jefferson broke it all down in a now-deleted TikTok over the weekend ... responding to a video that a former ball boy had made recently.
In the ball boy's vid, he claimed Jefferson was "always condescending" and was "the biggest jerk I met."
Jefferson revealed he did, in fact, often give the guy the cold shoulder .