It wasl a splashy arrival. Kimberly Guilfoyle, the new United States ambassador to Greece, landed in Athens on the private jet of a multimillionaire Greek American businessman. She caused a sensation at a Thanksgiving week dinner in a partly sheer black evening dress. When she presented her diplomatic credentials to the Greek president, Constantine Tassoulas, she told him she had previously been to Greece on a “fabulous honeymoon, but …” and then trailed off.