I heard this a couple of weeks ago from Fr. George Almeida, who came and filled in while my pastor was away. Really cool story.
A young boy went to the ice cream store. The waitress asked what he wanted, and he asked, "how much is the ice cream sundae?" She answered, "fifty cents" (obviously this had to be a good 30-35 years ago - at least). The boy started sloooooooowly counting his change. The waitress snarled to the boy, "Well, come on, let's go. I have 'bigger' customers to wait on, ya know!" He then asked, "how much is the plain ice cream?" The waitress, showing extreme signs of impatience on her face, snarled, "thirty-five cents". The boy once again slooooooooowly counted his change, then said, "I'll have the plain ice cream please." The waitress then got his ice cream and the boy paid her the exact amount.
After the boy left, the waitress went to clean his table. Underneath his dish was two nickels and five pennies. The waitress, growing quite the lump in her throat, realized that it was the fifteen cents difference between the plain ice cream and the sundae. He had enough to get the sundae, but wouldn't have had any money left to tip the waitress.