It gives the character unique dialogue with males, and increased damage. Speculation has been made that it means the character is homosixual, but it is just speculation, but it seems supported by the dialogue.
Yes, if you take that perk, you'll be able to use it to flirt with various men, I only know of three off hand, as I've never taken the perk. But if you go http://www.fallout.wikia.com and look up the perk, it should tell you who all the NPCs are that are affected by it. (Cass also has a dialogue line that is unlockable with that perk)
There's the male prosttutes at Gomorrah, Benny (not sure), Santiago, Old Ben, Manny Vargas, the human scientist at REPCONN Test Site, the hairdresser at The Kings (unconfirmed)