what is an insult that really insults?

An effective insult must fit the situation. No prefabricated phrase, just dropped into place, can have the same effect as an insult crafted to the lock onto the victim's indivuality. [cross-threading: another recent thread made the same point, in another context]

Disraeli once described the manner of Bishop Wilberforce as "unctuous, oleaginous, saponaceous." And the good prelate was ever afterward known as Soapy Sam. For every man there is something in the vocabulary that would stick to him like a second skin. His enemies have only to find it. -- Ambrose Bierce, Devil's Dictionary