X considered harmful

This one has already been well-documented on Language Log and Wikipedia. For computer scientists, the X0 is “Go to statement”, per a 1968 letter to Communications of the ACM by Edsger Dijkstra, but this phrasing was actually journalistically well-known well before 1968, which is likely why it was chosen as the title of the 1968 letter. Since the phrasing is not particularly idiomatic, it arguably did not become a snowclone until the “Go to” variation became well-known. All the variants of X are really particular to computer science writing, more specifically to programming languages or shell commands because of this origin: cat -v, csh programming, global variable, recursive make, considered harmful (my favorite).