looking for a trope/making new trope

I remember seeing a rerun of King of the Hill, where Bobby makes a special meals for John Redcorn on thanksgiving. He did the research and decided to feed him a turkey made to look like a human head. Redcorn points out that his people haven't practiced cannibalism for years.

I have seen this kind of moment before, where the character has done the research, but researched the wrong thing, or left out a key peice of information. Would this kind of trope exist and if so, what's it called?

Lost And Found is where you find tropes, YKTTW is where you make tropes.