Here are a few quotations (of insults) that are simple and powerful in their own right. And yet, they are all a bit oxymoronic!
“Deep down, he’s shallow.” (Anonymous)
“He had nothing to say and he said it.” (Ambrose Bierce, on a contemporary)
“He’s the kind of guy that can brighten a room by leaving it.” (Milton Berle, on a contemporary)
“A professional amateur.” (Lawrence Olivier, on Marilyn Monroe)
“He has delusions of adequacy.” (Walter Kerr, on a contemporary actor)
“A genius with the IQ of a moron.” (Gore Vidal, on Andy Warhol)
“An inspired idiot.” (Horace Walpole, on Oliver Goldsmith)
“A sweetly vicious old lady.” (Tennessee Williams, on Truman Capote)
Source: oxymoronica by Dr. Mardy Grothe.