Deliberate mistake: After jumping off the cliff, Dom and Letty's car rolls over violently several times and finally lands on its wheels. Letty sits calmly, safe and sound, not a single scratch or bruise despite not wearing her seatbelt and having survived by just grasping the handlebar above her head.
Deliberate mistake: During the chase with the mega magnet that attracts humongous armored trucks and all metal objects, surprisingly the people's watches, rings, jewelry, keys or belts don't move a single inch, thus allowing everyone to remain steadily on the ground instead of flying towards Dom's magnetized car. This allows for the hero to avoid killing innocent people, but it's all totally senseless.
Deliberate mistake: The F&F series always shows some amazingly advanced (and unlikely) technology; in this movie there is a big usage of electromagnets that are nothing short of miraculous. Not only they have a strength that would require them to have generators tens of times bigger than the cars they are on, and repel with the same ease as they attract; they also attract objects with varying° of precision and direction, all by turning their simple dial.