I find the words Kunt, Fucktard to be almost polite these days, my preference would go towards "You Piece Of FuKcing SHHHIIIT" as an appropriate slur.
Kunt/MoFo/Fucktard can be used in everyday speech without any problems in the UK, especially with speech retarded English language these days.
Where I grew up, I can remember pupils in my class back answering the teacher using the negative, "Fuck Off You Stupid Kint" and generally no offence was taken, however, the word "Shithead, Piece of Shit, Shitheed (as per dialect) often brought the wrath of a piece of bamboo wrapped in selotape!