The perineum. A retrospectively developed latinate variation on taint. Origionally referring to a brace of freshly killed rabbits, taint came to be primarily associated with that part of the rabbit anatomy most readily available to inspection when strung upside-down upon the end of a stick. Tatus is taint's more refined cousin, having been exorcised of its residual provincial overtones.
Rusty - "Dad, is it wrong to touch another man's tatus?"
Rusty Senior - "Not at all. Now cut away the gusset son - a tatal inspection is in order"