Not heard this word for years, my understanding of mush...dependent on how it is said it can either be aggressive to a stranger or a term of friendship to a mate, origin from Romany Gypsy. I've also seen it written as moosh. But really it was just traditional slang term.
As for it being an insult, i never ever understood it as such, although the word may have evolved.
Although i have never taken offence to being called a pikey, it by many would have certainly been seen as a greater term of offence than the word mush, not even sure if the latter slang is even used anymore.
You're right, it's not an insult. It's purely a gypsy/pikey word to say 'mate'.
A lot of Chavs now use it, mush.



