The text is in Swedish and translates to "Rock the arse off of the right[wing]". To explain the humour in this image is probably impossible to anyone who hasn't heard the radio skit "Bussen" (the bus) from Swedish comedians Bröderna Lagerståhl. I'll give a short story explanation though.
A man wearing a lapel pin with the above words is first harassed by a redneck, but manages to fool him that he's not a socialist. The redneck later becomes the guy's ally against two snobs from "town" who are also giving him a hard time for his badge.
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