A person so unattractive that the only time you would have sexual relations with them is if you were trapped on a desert island together - Desert Island Fuck.
A WAY TO DISCREETLY SAY SOMEONE IS STUPID; A BIG DUMMY.
IN REFERENCE TO THE 1970s TELEVISION SHOW "SANFORD AND SON", WHEN FRED WOULD CALL HIS SON LAMONT A "BIG DUMMY".