sandals that are worn regardless of the perceived importance or "social-status" of the event they are worn to.
the higher the importance or perceived social status the sandals are worn to, the more of a "fuck you" it is.
Example 1: I can't believe he wore his fuck-you-sandals to Jane's wedding at the Ritz Carlton!
Example 2: That weird guy in cubicle #202 wore his fuck-you-sandals to the company meeting led by the CEO. And he sat up front! What a douche.