Origin of “Too Clever by Half”
We say "by half" to emphasize the degree of something in an idiomatic way, and often as a slight on the person we're talking about. For example,
He's too clever by half. You're too complacent by half. He was too good a teacher by half for that school.
How did this phrase originate? What relevance does "half" have to do with the superlative nature of an attribute?