"Caca de toro" ?
This could be an interesting post. Your coffee cup says "caca de toro" in Spanish, that is because it has a double meaning (doble sentido)
But there are other words we can use:
"excremento", "heces" or "materia fecal" (If we are talking about in terms of Fecal material)
"estiercol", "bosta" or "abono orgánico" (If we are talking about in terms of manure)
Hope it was helpful
Is this a common expression in Mexico? I've never heard it in Argentina.
Sounds kind of Spanglish to me.