I always wondered what on earth McCartney was going on about in 'Mean Mr Mustard,' as part of the 'Abbey Road' album. Now I know! I came across this on Twitter, this is the story of the real man, who actually existed.
Mean Mr Mustard was a Glasgow Civil Servant who was indeed Mean!
His meanness was such that he would switch of the light when listening to the radio as "Because it was not necessary to see in order to listen." He also did indeed 'Shave in the dark,' This I can tell you having tried it, this is not a good idea!
Claiming he "Came from north of the border," he lived with his wife in Enfield, north London, but for some reason she, a deputy headmistress, found his behaviour unreasonable. I see no reason why!
The judge granted his wife a divorce.
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Now we know why the song was written but not why he put it on the album. 'She came in through the bathroom window' referred to a couple of girls who broke into Paul's house in St John's Wood next door to 'Lords Cricket Ground,' where they did indeed come in though the bathroom window and were arrested and fined. Quite right! These girls made the neighbours life a misery, here and at Abbey Road itself. I often saw them when delivering round that way. 
