Git: The History

Git is a relatively mild British slang term, used to denote a silly, incompetent, stupid, annoying, childish or senile elderly person.

Origin
The word git first appeared in print in 1946, but undoubtedly predates it. The etymology of the word is a contraction of "illegitamate" dating back to the 14th century. A shortening of 'beget', 'get' insinuates that the recipient is someone's misbegotten offspring and therefore a bastard i.e. illegitimate. In parts of northern England, Northern Ireland and Scotland 'get' is still used in preference to 'git'.

Use
'Git' is frequently used in conjunction with another word to achieve a more specific meaning. For instance a "smarmy git" refers to a person of a slimy, ingratiating disposition; a "jammy git" would be a person with undeserved luck. The phrase "grumpy old git", denoting a cantankerous old man, is used with particular frequency.

In Entertainment
The word was often used in the sitcom Til Death Us Do Part where Warren Mitchell as Alf Garnett would frequently describe his son-in-law played by Tony Booth as a "Scouse git". Micky Dolenz penned the Monkees song "Randy Scouse Git" on the Headquarters album after hearing the term on the programme. The group's British record company at the time felt uncomfortable with the use of the word so the song was issued as "Alternate Title" in the United Kingdom. John Lennon also uses it in the Beatles White Album song, "I'm So Tired." He says, "And curse Sir Walter Raleigh, He was such a stupid get," using the archaic version to rhyme with "cigarette."

Reference: Wikipedia