After a weekend of drinking beer, eating all those chilli dogs, poutine, and whatever else came in contact with your lips, shitzilla is what attacks you (usually on sunday evening) when you tremble as you approach the toilet.
"Oh man, Shitzilla's on the prowl, can you hear him growling?"
"*Whew* Shitzilla reallytook a round out of me that time"
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.