"Hair of the Dog" is the title track of Nazareth's 1975 album Hair of the Dog. It is sometimes called "Son of a Bitch" because of the repeated lyric in the hook ("Now you're messing with a son of a bitch"). The song is about a charming and manipulative woman who can get men to acquiesce to her every need. The singer is letting her know that she has met her match in him, a self-described "son of a bitch."

"Hair of the Dog" uses a talk box extensively during its bridge. The song's title, which does not appear in the lyrics, is a pun ("hair of the dog" = "heir of the dog" = "son of a bitch").

As a standalone song, it only charted in Germany, where it peaked at #44. In the United States, because the Hair of the Dog album was a top-20 hit on the album charts, the song received extensive airplay on album-oriented rock stations (despite "bitch" being a borderline profanity) and remains in the playlist of most classic rock formatted stations. 

In the USA, it was released as the B-Side of Love Hurts.