"He's no oil painting"

It is rather cruel to describe somebody as being "no oil painting". It is also inaccurate. Next time you go to use that expression about somebody, just remember that Heironymus Bosch and Pieter Bruegel the Elder painted in oils. Their people were hardly attractive but were definitely oil paintings. It would be more sensible to describe less than aesthetically pleasing people as being "no late period Picasso".