ديل الكلب عمره ما ينعدل

A dog’s tail is never straight.[1]

The lazy and incorrigible are never cured of their bad habits.

 In what can fairly be described as a well-deserved insult, an exasperated tutor from Luxor taught me this expression. It was among the only things I learned from him.

“Never,” it turns out, is relative, as seen in more colorful Syrian variants:

ذيل الكلب أعوج لو وضعوه في القالب 40 سنة

A dog’s tail is crooked even if it were put in a cast for 40 years.

ذنب الكلب بضل اعوج لو انحط في القالب مليون سنة

A dog’s tail stays crooked even if were set in a cast for a million years.

[1] This variant appears in: J. Hanki, A Collection of Modern Egyptian Proverbs (Cairo, 1897), 50. See also: J.L. Burkhardt, Arabic Proverbs; or the manners and customs of the modern Egyptians, second edition (London, 1877), 91.