The 59-year-old doesn't have a shy bone in his body ... uploading the snap Thursday while chillin' in a tub.

It's unique ... most people who see pics of Tommy first notice all the tats, but the eye can drift in situations like this, right?

Pam Anderson's ex captioned the pic, "Ooooopppsss." Yeah, we're not buying that either.

There were lots of comments ... his wife, Brittany Furlan, responded, "OH MY GOD," while comedian Ryan Sickler replied, "Does the camera add 5 lbs?"

Dating app Grindr jumped on the train ... "Wrong app, babe."

There was, of course, criticism ... some fans were disgusted, asking him to take it down. It's been 86'd from IG ... unclear whether he did it or the platform took action. The pic is still on Facebook.

Tommy had a follow-up ... with a pic of an elephant looking at a male model, with the caption, "How do you breathe through that little thing??"