To me a 'Good Lens' is acceptably sharp wide open, with decent contrast and colour. It's got low distortion, preferably barrel distortion rather than moustache or pincushion. The out of focus rendering is smooth and round. It's neither massive nor tiny, has a reasonably damped focus ring, a smooth and positive aperture ring and doesn't tend to come apart when it spends a week at the bottom of a bag.

By those standards, most of my lenses are good and a couple are bad. The exception to the rule is the Sigma 24/2.8 Superwide II, which is good by optical standards, but a little recalcitrant from a handling perspective.

I've owned a few 'bad' lenses. Still have 2 (Kenlock 135/2.8 screwmount, Soligor 35/2.8 screwmount) as they aren't worth getting rid of, and the Kenlock actually produces decent images as long as I'm willing to scan them, add contrast and sharpen.