Lady Killer/Fallout: New Vegas

Lady Killer is a perk for male player characters in Fallout 3, Fallout: New Vegas, and Fallout 4.

Fallout 3 and Fallout: New Vegas
In combat, you do +10% damage against female humans and non-feral ghouls. Outside of combat, you'll sometimes have access to unique dialogue options when dealing with the opposite sex, similar to the Sex Appeal trait. In Fallout: New Vegas it is supplemented by Confirmed Bachelor perk.

Additional dialogue options

 * Fallout 3
 * Nova in Megaton will provide you with the password to Moriarty's terminal.
 * Brianna in the Blood Ties quest will provide you with the password to Ian West's cell.
 * You can talk the AntAgonizer into stopping her attacks on the town and ending her feud with the Mechanist. You also get her costume.
 * You can talk Fantasia into stealing Dukov's key for the You Gotta Shoot 'Em in the Head quest. It is possible to do this without the perk though, but Lady Killer eliminates the possibility of a Speech check failure.
 * You can talk Agatha into giving you ammunition to help you during the Agatha's Song quest.
 * In Operation: Anchorage, you can calm down Specialist Olin and get more detailed information on questions. Also, the conversation will not end after each question.


 * Fallout: New Vegas
 * You can flatter Old Lady Gibson into giving you the Thrust control modules for free during the Come Fly With Me quest.
 * You can make Janet immediately fall in love with Jack during the Young Hearts quest.
 * A hooker named Dazzle in the courtyard of Gomorrah will have sex with you for 50 caps instead of 100.
 * You can flirt with Lady Jane to have her pay her debt to the Atomic Wrangler.
 * You can invoke some humorous dialog between you and the Lonesome Drifter; he informs you that he lived in Montana and his father left before he was born, the player has the choice of worriedly asking "Montana? Oh god, you wouldn't happen to be 17 would you?" to which he replies in the negative, and the player responds by attempting to change the subject.
 * You can compliment a ghoul or human female prostitute on lower Brimstone table in Gomorrah during How Little We Know in exchange for Cachino's location.
 * You can imply that Cass is flirting with you to which she will say your relationship will not go any farther.
 * You can access some unique dialogue options, and eventually seduce Light Switch 02 in Old World Blues.
 * In Old World Blues, you can talk to Dr. Dala about your breathing for the quest Coming Out of Her Shell.

Fallout 4
With the first rank of this perk, women take 5% more damage and are easier to persuade in dialogue. The second rank bumps to bonus damage up to 10%, makes persuasion via dialogue even more easy, and can be coupled with the Intimidation perk to make pacifying more easy. The third rank increases the bonus damage to an additional 15% and makes persuasion via dialogue and pacifying via the Intimidation perk are substantially more easy.

Behind the scenes
The term "Lady Killer" is slang, dating back to the 19th century, referring to a man who is very popular and/or influential with women.