Which American celeb, loved to brag that the term "Mayonnaise" was in honor of a family ancestor?

I believe it was Ed McMahon, but never proven.

I remember seeing McMahon say this on the Tonight Show. He also claimed that the pineapple was named after an early Hawaiian king, Pi-ni-ap-pali.

Right answer Sailracer.

History: When first invented, it was called Mahonnaise. According to the Oxford English Dictionary, the sauce got its present name of mayonnaise purely by accident through a printing error in an early 1841 cookbook. There are many conflicting stories on the origin of mayonnaise:

McMahon once asserted to Johnny Carson that mayonnaise was originally named Macmahonnaise in honor of this ancestor, referring to him as the Comte de MacMahon.[3] In his autobiography, McMahon said that it was his father who told him of this relationship and he went on to suggest that he was not certain of the truth of the story.[4]

The OED gives the origin of the word as " French: Perhaps from the feminine of mahonnais,adjective,from Mahon the capital of Minorca".Note the 'perhaps'