Holy shit! was an expression used in 1985, as a strong explicit form of saying "uh-oh" or "oh no". Marty was prone to use this exclamation when he was surprised. Such occasions included: watching the Libyans' sudden appearance; looking in his rearview mirror and noticing a rocket launcher being aimed at him; surfacing from a pond and realizing that the Courthouse Mall has been smashed; realizing that old Biff Tannen had been in the DeLorean time machine; and realizing that Clara Clayton had been meant to fall into Clayton Ravine.