Let's start off this series with a doozy. Perhaps the most offensive Spanish curse is "Me cago en Dios," which means, literally, "I shit on God." To soften this rather fuerte (shocking) imagery, there are lots of substitutions for "God". Think that middle-school replacement of saying "sugar" when you want to say "shit." (Here they say miércoles [Wednesday] when they want to say mierda [shit].) When you want to shit on something other than God, the options include:
Me cago en... I shit in/on...
...la leche ...the milk
...la mar ...the sea
...diez (sounds like Dios, god) ...ten
And should you want to make "I shit on God" even more offensive -- didn't think that was possible, didja? -- you can say Me cago en tu puta madre, which means "I shit on your whore mother."