There's nothing average about ''Average Joe: Hawaii'''s David Daskal. Whether jumping on a couch, tossing a watermelon into a pool, or reciting ''The Greatest American Hero'''s theme-song lyrics, the former mail sorter and star of a Spanish cell-phone ad (vagabond films.com) has stolen the show. ''I used to watch 'The Real World' and think, If I'm ever on a show like that, I'm gonna go nuts,'' says Carrot Top's twin. So how will he outdo himself? ''I hear Def Leppard might tour,'' he says. ''If I can sing 'Foolin'' with them, my life will be complete.'' The scary part? He's not f-f-f-foolin'.