You jest, but en passant to the king is a thing in many chess variants. Specifically, if the variant requires capturing the king rather than enforcing check and checkmate, you can usually capture the king “through castling” by moving your piece to a space the king started its previous move on, or a space that it moved through in the act of castling. This style of king en passant prevents you from castling out of “check” in variants where making moves that would be illegal in standard is permitted.