Lyric discussion by bbzzdd 

The song is clearly about a guy who does nasty things for pay. Not necessarily a hitman, but someone who does dirty deeds (roughing-up, adultery, murder) for cheap. AC/DC is one of the most straight-forward bands on Earth. Aside from a liberal use of double entendres, what you hear is pretty much what you get with them.

The first verse is about a girl whose high school principle (high school head) is banging her for the grades she needs to graduate. Bon's offering to take care of the situation for her (beat him up or kill him). The phone number is an Australian number (AC/DC are from Australia, duh). It's not a woman's measurements.

The second verse is about a woman whose man is cheating on her. Bon's offering to sleep with her for revenge. Essentially a gigolo or male prostitute job.

The third verse is about a guy who wants to kill his wife but does not have the guts to do it. Bon is offering to kill her for him, plain and simple. The "back door man" line always confused me, but I think it's safe to say Bon was using the wrong term and it was not some sort of offer for gay sex.

The outro is just a list of ways to kill people, with nods to other AC/DC titles (TNT, High Voltage). A "necktie" is when you slit someone's throat and pull their tongue out through the hole.

@bbzzdd Pretty sure the phone # is intentional meant to be the ideal female measurements...I took it to mean he only wants these type of women to call him or at least this would be his pay for doing the dirty deeds I think "it's safe to say Bon was" not using the wrong term, though it may make you uncomfortable he really would do dirty needs, for a fee

@bbzzdd AC/DC were known for their "double entendres", as we all know from the song "Big Balls". Sydney Australian phone numbers were 6 digits back then, but the numbers chosen are the alleged ideal woman's measurements.

An error occured.