The Rice University Neologisms Database

A frozen fruit drink David Letterman persuaded Rupert Jee to sell slurpies (flavored fruit drinks) at the Hello Deli, but after using the term so many times on the show, 7-Eleven told them that the word is copyrighted for their own drinks, and if Letterman or Rupert used it again, they would be sued. So Letterman changed the drink name to Flurpie. I’m guessing the fl- part is from flavor and the rest is a blend from slurpie. I'm not sure why he couldn't just call it a slushie because that's why they look like, but he probably wanted to come up with his own word. The fl- beginning also suggests some meaning of motion (sound symbolism) like some other words (flicker, flutter), perhaps because of the idea that a flurpie would normally be eaten with a straw.