Perhaps it was John Candy’s impeccable delivery? Or maybe because it had everyone asking ‘What the hell is an Orange Whip anyway?’
There is actually an alcoholic beverage called Orange Whip—made with rum, vodka, orange juice and cream. However, this is not the drink John Candy was referring to in the movie. The truth is, the Orange Whip in question was merely a carbonated orange soda-type beverage made by the now defunct Orange Whip Corporation (seriously).
A set designer on the film had a father who was Vice President of the beverage company and asked Director John Landis if ‘Orange Whip’ could be mentioned in the movie. The scene was then completely improvised by Candy. [source]