The actress posted on IG Tuesday -- a day after she hit the big 3-8 Monday -- and it was a simple shot of herself looking gorgeous and sipping on some bubbly. Her caption was telling as well, with AH simply writing ... "Champagne kind of birthday."

It also looks like Amber is in some kind of wine cellar here, 'cause she's surrounded by a ton of bottles on both sides -- which is also interesting considering her history with JD.

Fact is ... it was 8 years ago to the day that her then-husband Johnny got a call from his maid, who informed him that feces had been found in his bed at his Downtown L.A. loft -- which he ultimately decided had actually been left behind by Amber herself.

It was a whole saga at the time ... Johnny said he felt Amber had done this after she got mad at him for bailing on her birthday party at the time -- only to go to Coachella the next day and leave him with a "surprise" as payback. That was his POV, anyway.

Amber, for her part, denied she'd left poo in the bed ... insisting it must've been done by their dogs -- even though JD scoffed at that, saying it was far too big for such small pooches.

As silly as it sounds ... this was all testified to in court during their 2022 trial -- when Johnny sued Amber for defamation and (mostly) won. He went on the stand and gave his side of things ... while Amber did the same. Indeed, s*** was the subject of courtroom testimony.

A lot has happened since that trial ... let alone since the alleged bed-doo-doo incident. Amber has since moved to Europe and is living a relatively quiet life with her young daughter. Johnny, meanwhile, has been working on music and movies ... with middling success.

Fact is, Johnny hasn't quite had the mainstream Hollywood comeback he was maybe hoping for -- and Amber hasn't really done a whole lot either in the aftermath of the trial.