Wasn't the name of the ancestor of the Kennedys,Ceindeidig mac Lorcain,
supposed to mean "helmet head"? The 'eidig' part, from 'étid' - "clothe,
purportedly refers to Ceindeidig's unattractive facial features.
I think that famous ancestors tend to be a source of pride to people, even
if, or especially if, they have distinctive epithets. Certainly, many
important historical figures had strange nicknames, Charles the Bald, Vlad
the Impaler, Niall Glundub, Cobthach Coel.