The couple chowed down Sunday morning around 11 AM at a restaurant near the Beverly Hills Hotel -- where they were perched at the counter and having pancakes and eggs alone in the corner together ... this according to eyewitnesses.

We're told they were being cute and affectionate with one another, minding their own business -- and all was going well until a random lady asked for a photo with KJ ... whom, our sources say, shot the woman down ... pointing out she was eating and not up for it.

Afterward, Kendall's hired muscle stood guard while they continued to eat and whisper into each other's ear. Of course, just 9 hours earlier -- KJ and BB looked absolutely pooped.

Kendall threw a party at the Chateau Marmont ... and a crap ton of celebs rolled through. It was one of the big shindigs in L.A., with the super model dressing as the late Marilyn Monroe -- captioning her photo dump costume post "happy birthday mister president."

No sign of Bunny in her shots -- but he was dressed in formal attire as they drove away from the hotel around 2 AM this morning in the same SUV ... which makes this relative quick brunch turnaround somewhat impressive. These two were up and at 'em after a rager!

A couple takeaways ... Kendall and Benito are obviously going strong and tied at the hip, as they continue to roll together from coast to coast ... be it for the holidays, or milestones.

More interestingly, though -- they don't seem to feel the need to flaunt their relationship on social media. You won't find Bad Bunny on Kendall's page, and likewise for his channels. On both accounts, neither is featured ... so, technically, they're not even really Instagram official.