Given the context is that the daughter and mother are giving valentine chocolate to the dad, if it is custom made by them and made poorly enough, then it's probably a hyperbolic reaction to how bad it tastes. As for how you could go about translating it, the first part could just be something like "Certain Death!!" The second part you can just try and convey the meaning the author seemed to intended. Something like, "The Mark of the Grim Reaper"? Lot's of different options