Have to say that when I was teaching in the East End of London I never heard anyone called anything as fun as a pilchard. If only. Mildest form of abuse (for a woman) was to be called a silly or dozy mare. For a man ...probably a wally or a wazzock.
I got into trouble once with a pupil who had consistently misbehaved on a school trip to France. On the final day there were yet more misdemeanours and I was short of sleep, lacking in patience and close to throttling the child, but I carefully held my hands behind my back. And called him a wally. His parent complained about me, and my head teacher called me in for a discussion of the incident. After hearing the circumstances he said (and this was not a man noted for his understanding and sensitivity) "I do think on this occasion you were wrong to call him a wally. If I'd been in your situation I would have called him a ***&£*! idiot. The complaint will go no further." And it didn't.