Talking to friends last night the expression ‘en katt bland hermelinerna’ arose. This literally translates as ‘a cat among the ermines’, an ermine being a type of stoat or weasel.
The phrase originated in a couplet by Swedish performer Karl Gerhard in 1955. Karl Gerhard is one of Sweden’s historical entertainers who wrote songs and couplets as well as a large number of sketches, dialogues and monologues. During the Second World War, he wrote humorous pieces with strong anti-fascist statements criticising the Swedish government’s apathy towards Nazi Germany.
So, he coined the comical expression ‘en katt bland hermelinerna’. It’s not the same as our ‘cat amongst the pigeons’ which means somebody is causing chaos and panic. The expression refers to a person who has insinuated themselves into an environment where they do not belong, because they are not from the same social class. In other words, someone who isn’t fancy enough for the rest of the people in their company.
As far as I am aware, there is no expression for this in English. But I hope I’m wrong. Can any of you readers help me out here? Do you know of an English equivalent?
Watching the Swedes 
‘Mutton dressed as lamb’ ?
Could be….although I interpret that one to refer to an old person trying to look young. But it does refer to the same type of phenomena- trying to fit in…
Similar to “a wolf in sheep’s clothing”, but not quite.