Conrad Murray -- Joan Rivers Death Doesn't Dirty Propofol

Conrad Murray is weighing in on Joan Rivers' death ... because, after all, he IS an expert on Propofol.

Murray was nursing a frothy drink in Barbados when a photog screwed up the question ... she suggested to Murray Propofol was somehow the cause of Joan's death ... which is wasn't.

Nevertheless ... Murray sang the virtues of the drug, and then launched into his tried-and-untrue argument that he was framed by L.A. County prosecutors in Michael Jackson's death.