I remember being really fond of the phrase cheesemonger as a random insult without really knowing what it was when I was maybe 8-10 years old.

"That guy crashed his car because he was playing with his phone, what a complete cheesemonger!"

Only when my dad said, "do you know what that even is?" "No..." "Then why are you using it?".

I immediately thought it might be something really rude, so stopped.

It's literally just someone who sells cheese. No idea where I picked it up or thought to use it as an insult. All I can think is we also have the derogatory word 'mong' to refer to people with learning difficulties, which is used as an insult.

Maybe my brain mixed up the two without realising?