As adjectives the difference between yappy and zappy
is that yappy is of a dog, yapping in an annoying manner while zappy is (informal) lively or energetic.
yappy
English
Adjective
(er)
Of a dog, yapping in an annoying manner.
Very talkative; talking foolishly or at length. zappy
English
Adjective
(er)
(informal) lively or energetic.