(this is an outsider's understanding; I have not played the game myself)

There are two perks you can get in the game: "Lady Killer", which grants a charisma buff (or something like that) when talking to female characters, and also allows you to do +10% damage to female characters. "Black Widow" grants the same charisma (or whatever) when talking to male characters, and the same +10% damage to male characters. It's possible to get both of these perks at the same time.

It is my understanding that the previous game, Fallout 3, prevented anything but heteronormative interactions ie to romance a female NPC the player had to choose a male character, etc. To quote hbomberguy, "It implies that Bethesda doesn't think gay people exist." By contrast, New Vegas allows any character to take either of the above perks, or both at the same time, allowing one to roleplay as a gay or bisexual character to an admittedly tiny degree.