Crapzilla is an exclamation (also called an interjection) that expresses strong emotion; when plans, intentions, things, life go epically wrong. This exclamation stands on it's own, and in writing it is followed by an exclamation mark. Crapzilla is to be used when a simple "crap" does not sufficiently capture the over the top, grand, larger than expected, as large as Godzilla fail that you are faced with.
"Crapzilla! Someone just wrecked into my brand new car I just bought with my life savings!"