Turd. Fex (or faex) is the singular of the Latin word feces (or faeces). Although feces has entered English as a mass noun, fex retains the original meaning of a single, discrete piece of shit.
John said his girlfriend
Sarah was a fox, but when I pointed out her lumpy shape, terrible odor, and weight of only 18 ounces, he admitted that she was, in fact, a fex. He cried and cried after we flushed her, and claims to this day that she was the only woman who ever truly understood him.