As has been said, nearly always said as three seperate letters.
Think it stems from a reluctance by drivers to say “had a good night out in my man the other night” or perhaps " “I need to climb three steps to get inside my man”, you get the picture I’m sure.
When I first started driving I walked into our garage at the start of my shift and said to the fitters, “could you help, I’m having a bit of trouble with my man?” As quick as a flash one stood up and in his best camp impression said “not you too sweetie, mines been a complete ■■■■■ all week” oh how they all laughed