Since this person is trying to do right by you, it's probably best to approach it by first acknowledging their attempts to be helpful before asking them to stop. I'd recommend saying something like:
"I notice you've been sticking up for me when ______ (instance/example), and I appreciate the intent behind you doing that for me. However, I'm not bothered by _______ and I'd prefer to be the one to say something if I was."
The key to not making this relationship turn ill (especially since this person seems to be a workplace acquaintance) is to pat this person on the back for attempting to be your ally before telling them that you'd prefer to fight your own battles. While you may not actually be thankful for their attempts, it'll make the rejection a bit easier for them to handle (because at least you're saying you appreciate their effort).
tl;dr: thanks, but no thanks
On the side of approaching those who were "scolded" by this person, they'll probably warm back up to joking around after a while of not having this third party run interference (especially since you seem to like to joke about it yourself, and that's sure to lighten them back up to it).
I'd avoid telling them that the acquaintance was out of line because, again, he was trying to help... Plus, it could reflect poorly on you if it got back to him that you were actually really put off by his actions, and end up causing tension on your relationship.