1. A desire to drop a fecalith deposit in a nearby toilet.
2. An insatiable craving to let fecal matter exit the body.
3. Wanting to take a dump.
I walked into the Porta-Potty and saw that the crap had crested the hole in which it sat, whence seeing it I lost my crappetite and proceeded to leave.
The need or want to eat certain foods because of the pleasure you receive from crapping it out. For example, spicy food because it burns your asshole or garlicky beans because you can kill trees with your gas and peel the paint off the walls when you blow up your bathroom.
Example 1: I have a real crappetite for that ghost pepper sauce, there's no better buttholeburn!
Example 2: I have a real crappetite for baby food because how it eats isn't as important as how it craps.