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GCE is an acronym for "gross conceptual error". Originating in the nuclear navy, the acronym is used to point out when someone's logic is severely flawed.
Ted: You'd think that the water out of the water softener would taste salty with as much salt as we add to soften it up.

Ralph: Dude, GCE. The salt doesn't go into the water, it replenishes sites on the ion exchanger!
by Kate Sjostrand February 19, 2008