rigidly flexible
I am very disappointed with this list – Almost half are NOT oxymorons (eg “casual sex”). Whoever screens these does not understand what a true oxymoron is. The two words (usually adjective and noun) when taken alone must mean or imply something directly opposite of the other, such as “jumbo” (implying big) and “shrimp (implying small), “Casual” by itself does not evoke any meaning in the same context as “sex”.