The difference between Pathological and Well-behaved

When used as adjectives, pathological means pertaining to pathology, whereas well-behaved means having good manners and acting properly.

check bellow for the other definitions of Pathological and Well-behaved

Pathological as an adjective (medicine):

Pertaining to pathology.
Pathological as an adjective (medicine):

Relating to, amounting to, causing, or caused by a physical or mental disorder.
Pathological as an adjective (mathematics):

Having properties which are counterintuitive or difficult to handle.
Pathological as an adjective (computer science):

Having properties that cause unusually bad behaviour, especially regarding correctness or performance.

Well-behaved as an adjective (of a person or animal):

Having good manners and acting properly; conforming to standards of good behaviour

Examples:

"The boy is well-behaved and is seldom naughty."
Well-behaved as an adjective (mathematics):

Having intuitive, easy to handle properties, especially: having a finite derivative of all orders at all points, and having no discontinuities.