Any kind of word that ended with -py, -ie, -ty are cute because of the sounds refer back to infant talking. for example the cute word of comfortable is comforty ; and the cute word for cute is cutie.
Main Entry: poopy
Part of Speech: adjective
Definition: depressed; ineffectual; also spelled poopie
Example: I’m feeling poopy and just want to watch TV.
Etymology: 1957; perhaps shortening of nincompoop or euphemism for shitty, from poop ‘excrement’
meanings from dictionary.com