I saw KWhazit's note about Spekkio's line "バターにならないよう、気をつける" -- translated to "I'll pay attention so you can't cheat." -- was actually "Be careful not to become butter" in the original Japanese, but was unsure of the origin of the phrase.
That's because it dates back to 1899 and a story that isn't seen much nowadays:
https://en.wikipedia.org/wiki/The_Story_of_Little_Black_Sambo(I heard as a kid by my mom, who'd heard it from her mom. It was told to me as the story of a brave little boy who outsmarted four tigers AND got an awesome pancake breakfast! None of the controversial elements were included.)
It refers to the four tigers in the story that chase each other around the tree so many times that they turn to butter! Spekkio is teasing the party with a similar fate