Upon making eye contact with Edward and Bella's newborn daughter Renesmee (Mackenzie Foy), Jacob imprints on her. According to the "Twilight" fandom wiki, "Imprinting is the involuntary mechanism by which Quileute shape-shifters find their soulmates."
It begins as a protective stage, but the imprinter falls in love with the person imprinted on, and the two often end up together. Much like the initially infuriated reactions of the Cullen family, fans were uncomfortable that the teenage Jacob imprinted on a newborn.
On one thread discussing the imprinting, u/AnnaK22 said, "Imagine if your parents had a close friend who probably cared and babysat you as an uncle, but in the back of his mind, he always thought about possibly asking you out when you turned the legal age."
This is the stance that most fans took, with u/TKMLtheStar saying that they were unable to set aside their morals and "view it through the 'morally ambiguous fantasy' lens" because it went too far.
The uncomfortable imprinting moment, at the very least, gave fans the iconic "You nicknamed my daughter after the Loch Ness monster?!" line.
