Looking for material for my MA thesis, “Injuries and Battery in Tannaitic Law” – and thus avoiding working on the actual thesis – I came across this entertaining snippet from the recently published S. Emanuel, Teshuvot Maharam meRothenburg vaHaveirav, §308 (pp. 641-642, author unknown):
One who calls his peer a mamzer, should leave the synagogue, and fast Monday and Thursday and Monday, and receive lashes after every fast, and ask for forgiveness at the last one, and give 12 dinar to the Kahal, and walk on (perhaps: to) his (the plaintiff’s) mother’s grave in the presence of 10 (men) and say (at the grave): “everything I spoke against your honor (kevodekh) was a lie.” And (the insulted party) can waive his share and the Kahal can waive their share as well. And the same law applies to a woman, but she is not whipped but she should pay the plaintiff 5 dinar for each lash, and the same applies for every law. And this is the case if for instance she is a widow, but if she is married, and owns no property, then she should write (a promissory note) that if she is widowed or divorced – she will pay. But “A Whore’s son (הורן זון)” is not like “Mamzer.”
Emanuel quotes the Nimmukin of R. Menahem of Mirzburg, the laws of shaming (106b), in n. 4:
There is no law concerning calling a man a whore’s son, since all he said was: you are a son of a whore, and perhaps his mother was simply promiscuous, or perhaps she was not married, but he should not(?) degrate himself and prostrate himself on his mother’s grave.
Two interesting items here are (1) there is a grave and severe penalty for calling someone a Mamzer, although Talmudic jurisprudence rules quite unequivocally that shaming with words does not count as shaming, and (2) that the offence was apparently directed not at the person being shamed but at his mother.
This of course leads one to suspect that in fact this was a penalty for calling someone a “son of a whore” and not simply a Mamzer. A mamzer could have come from any number of forbidden unions, all odious but not all casting shame upon the mother – the child of a rape victim, for instance. But calling someone a “son of a whore” insults their very own mother directly, in which case redress of the injured party is called for.
My guess is “son of a whore” was just too common an insult to force anyone who uttered it to drag him/herself over to the graveyard and apologize to the dead mother. But it might also mean that in this cultural milieu, Hebrew insults were stronger and more real than German ones.
The Talmud Blog 
Calling someone a mamzer goes beyond mere shaming, for the mamzer is excluded from the congregation and cannot marry into it.
Does this mean that a mamzer should marry a non-Jew? I’ve read that mamzerim should marry mamzerim, but mamzerim are still Jews. Would this not mean that in order to not marry into the congregation, you would need to marry a non-Jew?
A convert, that is, or another mamzer.
I was about to comment as above, but Zohar beat me to it. Being a mamzer has horrific halachic consequences. In addition, a mamzer’s children are also tainted.
(1) Unless you can prove your charge, it’s not much more than shaming. THat’s why the penalty is for shaming.
(2) If your mother was in fact a whore, chances are you are a mamzer. I agree that there are other ways to become a mamzer but they are less connected with the mother of the shamed person.
I am interested in your reasoning for “If your mother was in fact a whore, chances are you are a mamzer.” Thanks.
If the mother was married and at the same time engaged in professional extramarital sexual activity, the offspring of such activities would be considered a mamzer.
Only if she was whoring with a Jew.
גוי ועבד הבא על בת ישראל, הוולד כשר–בין בפנויה בין באשת איש, בין באונס בין ברצון
Since there are tremendous legal ramifications of being labeled a mamzer, so too the shame associated with it is much greater than in the case of the accusations hurled against the mother that she is a whore. If the mother was unmarried, there are no legal ramifications of her being a whore, and if she was married, it is still only a possibility.
Why apologize to the mother, then?
Good question. First of all, when he calls his fellow a mamzer, he is actually accusing the mother explicitly of transgressing a biblical prohibition. Secondly, there is a legal principle that one who commits a grave offense is held accountable for smaller offenses which might have been overlooked otherwise. Alternatively, we are throwing the book at him.
The last point, that the language might be important, seems rather likely, if one looks at the use of vernacular expressions in Ashkenazic literature of that time. German was for everyday use, but the moment it becomes halakhic, German does not occur on its own, but is either a translation of the Hebrew term or is translated by a Hebrew term that can then be traced in the halakhic debate.
emes!