A vagrant whose charges in a 2010 Union Square sex ­assault were dropped because prosecutors deemed the victim too drunk to be a ­reliable witness has allegedly struck again — this time on a Midtown subway platform.

Riger Mayanduena, 36, was busted Friday for allegedly raping an intoxicated woman at 4 a.m. on a ­deserted Herald Square ­­B/D/­F-station platform.

Mayanduena was charged in 2010 with sodomizing a woman on a sidewalk near Union Square, sources said.

But he ended up just being charged with stealing the woman’s credit cards.