git Noun. An idiot or contemptible person. Although more commonly used, it is a variation of 'get'. Derog (UK Slang)
get Noun. An idiot, a despicable person. Cf. 'git'.
http://www.peevish.co.uk/slang/

Under the expletives thread, we discussed that the sound of the word has more to do with its success as an expletive than the meaning of the word. "Git" is a good example of a word which sounds aggressive, just because of the combination of letters.

Although it is derogatory, the word has been reclaimed and sanitised to a certain extent, particularly in the context of "old git". I have heard people saying "I'm becoming an old git" or "We're becoming old gits".

I suspect that the generation that thought of their elders as old gits are now realising that they are now becoming their parents!