Ryan Lochte Parties It Up in London -- Breaststroke, Anyone?

Nothing says party time like a pair of boobs in your face -- which is exactly how 11-time Olympic medalist Ryan Lochte celebrated in London last night.

According to sources, Lochte -- along with American teammates Nathan Adrian, Cullen Jones, and Matt Grevers -- hit up Chinawhite nightclub in the Big Smoke around 11PM ... and left around 3:30AM.

We're told they drank gold bottles of champagne all night -- obviously -- and even ordered some Patron and Grey Goose for good measure.

But they didn't leave empty-handed -- they piled into a cab with several, very excited females ... one of whom sat on Lochte's lap, placing her fun bags a mere nuzzling distance away from his face.

Meanwhile, Michael Phelps was partying a few miles away -- with his medals.