Ex-U.S. Navy Seal Robert O'Neill posted a photo Saturday of himself wearing a shirt from Sylvester Stallone's clothing store -- the Sly Stallone Shop -- featuring one of the actor's most iconic characters in an iconic shot ... Rambo taking his mug shot in 'First Blood.'

The American hero -- who's credited with firing the head shots that took down bin Laden -- also shouted out New York's finest in his caption, saying ... "The only guy with a better mugshot than me is Rocky! In the presence of badasses: Rambo and the NYPD!"

Funny enough, Sly's clothing IG account gave him some love back, re-posting his pic and saying ... "Truly an honor to have American hero @mchooyah Robert O’Neill wearing our Rambo mugshot shirt."