The incident recently went down in Astoria, Queens at a bagel shop called New York City Bagel Coffee House -- and, apparently, one of the customers who was wearing a mask noticed this gal without one while coughing, not covering her mouth ... and going mask-less.

The masked patron suggested to one of the staffers that they enforce a mandatory mask-on policy while inside the building -- and after overhearing her complaint, this woman lost it.

You can see for yourself what exactly she does and how she starts to conduct herself -- but here's a hint ... it's a lot of childish name-calling and then straight up flagrant coughing. It's crazy, 'cause once this woman turns around and sees she's being recorded ... she makes a face that basically says, "S***, I've been caught on camera acting like a jackass."

She sure was, and not only that ... people online are ID'ing her and finding out where she works, etc. The typical 'Karen' treatment if you will, only this is the COVID-19 edition.

But wait, there's more ... according to the woman who was coughed on, the employees didn't do a damn thing and they STILL served this wacko ... supposedly, not even checking on the victim or anything. That left the cough-ee furious and vowing never to return.