Or twist in general in movies.
1. The Gambit film from 1966
This is an extreme version of "if it had happened": Michael Caine character is fantasizing about great heist, and only aftre 45 minutes (!) one realizes that:: then the "reality" begins, and everything goes wrong, just the opposite of the plan.
2. Wild Things (Or Sex Crimes, film from 1998)
Several twists. It has a sequel.
The Crying Game (1992) - Stephen Rae, Forest Whitaker, Miranda Richardson
("... Halfway through, the movie ambushed its audience: after skillfully getting the viewer to empathize with an interracial heterosexual romance, the film — in a highly touted "surprise plot twist — "turned the tables on audience expectations by revealing ..." )
Zebra Force trash B-film from 1976, i Saw it on bad quality copz on Film+ channel...
White war veterans pretend to be black bank robbers (with masks), and at the end it turned that the leader was black (wearing a mask, in disguise as their war commander /who actually died in field hospital in either Corea ir Vietnam/).