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Noun, a little hunk of something delicious and sinful; a guilty pleasure; something fattening and shameful to eat. Can also be used to describe a person who is naughty or too good looking or too over-the-top. Delicious, obscene.
What is that chocolate mess you are eating? -Oh, just a little sin biscuit I whipped up.

or

Did you see that hoochie outfit she's wearing? -That girl is a sin biscuit!
by anthnerd November 13, 2009
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