On many of his later films, W.C. Fields took to arriving on the set with a thermos bottle filled with straight gin. After every scene, he would dart for the thermos and refresh himself.
The producers, fretting over their schedule, begged him to refrain from alcohol. They even promised that when the film was done, they'd take him on an all-you-can-drink spree at the tavern of his choice.
Fields denied that the thermos contained gin. "It merely contains pineapple juice," he told them. "It soothes a slight stomach discomfort I've been experiencing." This fib, of course, fooled no one.
One day when Fields wasn't looking, a prop man grabbed the thermos, poured out its contents and refilled it with real pineapple juice. A few minutes later, when the comedian came over and took a swig, he was horrified. He spit the offending liquid out and screamed…
"Some bastard put pineapple juice in my pineapple juice!"