I saw it on two movies, and both times it was deeply unsettling: it is the second half of the movie, the protagonist, a cute girl who has a longtime boyfriend who currently is a few timezones away, meets a intriguing, sexy bad boy and is about to sleep with him. Miraculously, the girl does not need to cheat her nice and wholesome boyfriend: five minutes ago (in movie time) he just called her on the cell phone and told they were breaking off because whatever. So, soon there is a scene where she sleep with the mysterious etc. dude, and the plot moves forward, and the audience does not need to worry that the girl is a cheater.
It is a double cheating, and the victim is the movie audience and the movie coherence.
The two films in question where The Devil Wears Prada and Veronica Mars and in both the plot point was so obvious and opportunistic that it soured the whole film for me in each case. It is really an extreme case of movie producers wanting to have and eat the cake at the same time: the girl can switch from a boring guy to an exciting one, and she does not need to take responsibility for dumping the sensitive moron. It is just too cynical.