Has hunky Survivor II star Colby Donaldson gone sex crazy, or was he just making up for lost time in the Outback?

Colby shocked eyewitnesses at the New York nightclub Lotus by dirty dancing with well-toned Alicia, 33.

"It was a very sexual performance."

"They posed like a loving couple for a photographer before joining fellow Survivor Amber at the bar. It was a really swinging evening!"

But it didn't stop there, says the eyewitness. Before the night was over, Colby sneaked into the men's bathroom with Survivor II hottie Amber, 22 -- and was caught making out with her!

"When Amber showed her sexy side, Colby jumped on it," says the eyewitness.