Ryan Lochte Ain't Buyin' That Michael Phelps is Retired for Good

Liar, liar, Speedos on fire ...

Ryan Lochte says he just doesn't believe Michael Phelps is done with competitive swimming -- despite the fact he filed official retirement paperwork earlier this week.

Phelps' Olympic teammate was leaving Catch in West Hollywood on Monday when we broke the news to Lochte that MP formally removed his name from the U.S. drug-testing program ... which essentially means he can't compete at the Olympic level anymore.

HOWEVER, Phelps did the same thing back in 2012 ... only to put his name back on in 2013. So ... yeah.

Clearly, Lochte ain't buyin' the retirement thing -- which should probably scare the hell out of Team Australia.