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A phrase used to describe almost any situation where something is growing or increasing in size, depth, shape, weight, or awesomeness. It can also be used instead of "the plot thickens" or "this looks bad".

First heard on "Frat Party At The Pancake Festival" DVD, Phoenix (of Linkin Park fame) held up a tip jar and said, "It's getting fatter, the kitty is getting fatter!", referring to the exponential increase of spare change as time went on.
1. "So I checked my bank account. I now have almost $500! The kitty is getting fatter!"

2. "So I'm almost done redecorating my room. I got new curtains and hung up some Christmas lights." "Wow, the kitty is getting fatter."

3. " it turns out, Stacey thought she slept with Mike, but she actually slept with his brother, who was passed out in Mike's room." "Holy shit." "But that's not all..." "The kitty is getting fatter?!"
by anonymush September 23, 2009
Happy St. Patties Day!