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1 definition by Dr. Cole Kennedy Ziebarth, IV

 
1.
A girl who acts like a dead fish in bed. Possum(girl playing dead) sack(bed)
I was hooking up with Bobbie Sue McGillicutty the other day, she was a total possum in a sack, she just laid there and did nothing as I was giving her the best 2 minutes of her life.