This would be a lot easier to read if you fixed up the formatting. Ficwad seems to have eaten some of your tabs. ...Ficwad needs a tab-free diet!
"Underbelly" is one word, but dark and plastic? Unique.
Do you mean "tapped" or "taped" to her mirror?
I think "fatass" is one word too.
"Its" does not need an apostrophe.
Hmmm... Where to post this indeed. Have you considered Horror? A few foreshadowy tweaks to the earlier portion and it would fit right in. If I were you, I'd allude to the idea that the woman's eating habits kept her body well-padded, but not say what those habits were. This isn't a humor piece, really, though the quirky last line would close it off nicely.