A lot of films with Peter Sellers is what I call fun.
-"What's  New, Pussycat?"
-"Casino Royale"
-"Dr. Strangelove..."
-the Pink Panther movies
-"The Magic Christian"
-"The Party"
-"I Love You, Alice B. Toklas"

There are some other fun films.
-I agree with "The Rocky Horror Picture Show" because it was turned into an interactive film.
-Scrolling through all of John Waters' films, "Polyester" is the most fun because of the famous "Smellovision" cards.
-William Castle films like "The Tingler".
-"It's a Mad, Mad, Mad, Mad World".  That is fun to watch. 