John Mulaney is usually beloved by all, but right now — he’s getting slammed big time … all because he let Dave Chappelle open for him, and the guy told “anti-trans” jokes.

Here’s the deal … John had a comedy show Friday night in Columbus, OH — where phones were locked up in a pouch so no one could record — and according to folks who flocked to social media afterward, DC was a surprise guest who did a set before John came out.

A lot of these people say they felt ambushed by Dave’s presence, especially since he allegedly went on to tell what they characterize as transphobic/homophobic jokes.

The argument is that these paying customers came out to see JM — not Dave — and many of them are either part of the LGBT crowd, or consider themselves allies … going on to say they never would’ve purchased tickets if they’d known Chappelle was going to show up.

Of course, this all dates back to the controversy over his Netflix special, “The Closer,” which some have said is transphobic — despite DC denying that, and the streamer sticking by him.

As for what exactly was said that’s transphobic (in these users’ minds) … you’d be hard-pressed to find anyone who actually detailed the crack(s), but someone finally did. The supposedly harmful joke was about the stage crasher and the gun/knife he had on him.

Dave apparently said something to the effect of … it was a knife that identified as a gun, which some took as an allusion to gender fluidity — and sure, that’s a fair assessment.

He moved on from that — this after getting laughs, it seems — and then made a joke about a couple of audience members he speculated might be gay … adding, not that there’s anything wrong with that. Apparently, that’s about all that was said … but it’s got people up in arms.

We’ll say this … Dave does seem to be obsessed with joking about trans topics — he did so during his Hollywood Bowl sets a few weeks ago … and even said something about the alleged attacker, Isaiah Lee, joking that it was a “trans man” after he was tackled.

As for John, he’s said to have given Dave a hug … but hasn’t said anything about the controversy bubbling up now. He’s pretty private — don’t hold your breath for a statement.