Some friends and I went camping one time and we ended up getting a cooler that didn't keep things very cool. So when the ice melted and the bag of frozen hamburger patties broke open, the cooler and all the remaining food in it became saturated with a pinkish-red juice-like substance which we called "beef juice."

Needless to say, much of that weekend was spent making sexual innuendoes related to our newly-created term.

This also reminded me of the "beef curtain" metaphors used in the movie Welcome to Woop Woop.