Man, where to start with this one. The story goes that a crew of these fellows showed up at a farm and abducted a man, Antonio Villas Boas, taking him aboard their craft. He was taken to a room, stripped, and made to wait. An alien woman showed up without her clothes on and they did, well...it. Afterward he waited around, watching some of the beings talk, and tried to steal what he thought was a clock before they stopped him. Then they let him go.
Boas went into great detail about his experience. There are other witnesses including his brother, who, together, watched a ufo the night before, and a doctor who examined Boas afterward because he was all blistery and radiated and stuff.