Here in Sweden, in as a society where honor was a far bigger deal than now, all serious insults and slanders were punishable. Scandinavia did not yet have national laws until the late 13th century in Norway, mid-14th century in Sweden and after the Middle ages in Denmark. The laws in force were provincial laws. Because there were no libraries of case law to refer to, the laws tended to give many specific examples in order to illustrate how the law was to be applied. They also had a tendency to enumerate very specific crimes, like "tying someone to a tree in the forest and leaving them there", or "stealing before midday" (a more severe crime than stealing in the afternoon).

Anyway, the oldest preserved provincial law is the Older Westrogothic Law (or Äldre Västgötalagen), which was written down in the early 13th century but has linguistic features that show the text itself is older. Anyway, this law even distinguishes two different kinds of insults - oqvæthins orþ ('wicked words' sort of) and firnær orþ ('nasty words'). The punishments are about the same, and the words similar in content, but the latter seems to involve sexual insults to a higher degree. Anyway, here they are:

bykkiuhuælp Bitch-puppy - Same intent as 'son of a bitch'

fraelsgivas - 'Freedman'. Applies only to people born free. Harassing former slaves for being former slaves was fine.

þu rant en firi enom ok hafþi spyut a baki

'You ran alone and had a spear against your back'. The meaning of this is unclear, multiple interpretations exist. Such as they were a coward who fled battle, or an escaped slave.

maðær sarþ þik - 'A man bedded you' - [to a man] This one's less ambiguous.

þu atti þin viliæ viþ ko ællar mæræ

'You had your way with a cow or mare' - Bestiality.

þu atti moþor þina - 'You had [sex with] your mother' - A real cross-cultural one, this.

þu reet a quiggrindu løsharæþ ok i trols ham þa alt var iamrist nat ok dagher

[To a woman:] 'You rode a cattle fence gate with loose hair and in the shape of a troll when it was even between night and day' [i.e. midnight] - This is an amazingly specific and supernatural accusation.

firi gæræ kono ællær ko - Implying a woman is an "enchanter of women or cows". I.e. a witch.

hortutu - [To a woman] Whore-tit.

þu atit faþur þina - [To a woman] You had sex with your father. Or..

strukit hava barn sit - Having driven away her child. [may refer to abortion] Or..

hava myrt sit barn - Having murdered her child.

Some more oqvæthins orþ from Biærköæ rætter (or Bjarkey law in English), the oldest town law of Stockholm:

morþæri - Murderer.

liuari - Liar.

morþbrennærei - Arsonist. (literally 'murder-burner')

forsleghin herriæns son - "Whipped son of the devil" The word for 'devil' here (herjan) originally means 'lord' and is a kennig for Odin (See Gylfaginnig §3: "Herran eða Herjan"), who became equated with the devil in the Christian period. (the other form herren/herrann became the one used for the Christian god)

hwnzæmæ son - Literally 'son of a bich'.

horkono - Whore (if directed at a "good woman")

skukiu - Harlot

trolkono - Witch.

fordæþa - Enchantress. Sounds nice to modern ears but it's the same thing a accusing someone of witchcraft.

The Bjarkey penalty for these insults was set at 6 marks. By comparison, entering someone's cabbage patch and stealing cabbage was 3 marks. And 40 marks was the cost of "redeeming one's neck" for crimes they'd otherwise hang for. (such as murder, or stealing from someone while they were in the sauna) Robbing someone in the street was 12 or 6 marks depending on if it was done before or after midday. (6 and 3 for low-valued thefts) So it was a pretty significant sum.

In terms of ethnic slurs, one that's persisted from the Middle Ages to the present day is "Norrbagge" - Norwegian Bagge. Usually the term bagge means ram or male goat, but here it's theorized to have had some dialectal meaning like 'sheep testicle' that's been lost, because 'bagge' is not really much of an insult otherwise. It's not a very serious insult today but in the Middle Ages a king once ordered that anyone who used the term against the Norwegian king or his entourage while visiting would be executed. So it must have been rather serious at the time.