These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Pat's Trigger for his stalking of the ex is "My Cherie Amour", a song about a guy who loves a woman from afar. Given that he's got a restraining order against him forbidding him from even being near the school she worked at as a teacher and she won't give him the time of day, she's as unreachable and distant to him as the woman in the song was to the singer.
Pragmatic Adaptation: The film and the book don't diverge much until about halfway through, then go on completely different paths. For example: in the book, the dance competition takes place much earlier in the plot, is organized for troubled teens (making Tiffany the odd woman out in more ways than one), has no prize beyond participation (and has no bet riding on it) and in the end has little effect on the plot's resolution beyond Tiffany and Pat's relationship. Neither does Nikki show up.