It seems my mind fine-tuned the phrase without me noticing it, for years I’ve thought of it as:
"Never attribute to malice that which is adequately explained by stupidity incompetence."

It hits a little harder, I think, because incompetence should be vincible, a condition that can be overcome, implying that it’s a choice, a lazy indifferent choice, a mediocrity.

THE BRIAN
NAMED ITSELF
THE BRIAN
(and he would have gotten away with it, too,
if it hadn’t it been for you meddling kids)

Well… since most of the big ones are taken, I’ll throw in:
“Tu madre era una hamster, y tu padre olía a saúco.”

EDIT: Actually, now that I remember, the Spanish from Spain have some breathtaking insults, such as:
“Me cago en la leche de tu madre” - “I shit in your mother’s milk”.