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.
Singing out loud while listening to music with your headphones on. Whereas the singer gets the benefit of the music, those unfortunate to be standing nearby are subjected to an unaccompanied (and invariably crappy) rendition of the song.
Smitty: Did you go to the museum to see that exhibit on French Impressionists?
Austin: Yeah- there was a line out the door! Who knew art was so CRAZILLA?!
Smitty: Shut up.