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1.
Milk that is past the "use by" date printed on the container. It will smell bad, taste sour, and will begin to form large nasty chunks. If ingested, can cause many long hours of vomiting and diarrhea.
"Hey you didn't drink that expired milk in the fridge did you?!"

"That was expired! Ew, now I'm going to get sick!"
by Ashlie Mae January 14, 2012