Why does Winston hate Julia before he even speaks to her in the book "1984"?Part 1, Chapter 1
The main reason Winston hates Julia is because she is alluring to him, yet he knows he can never have her.
Julia wears the sash of the Junior Anti-Sex League in a paradoxical way, "wound several times around the waist of her overalls, just tightly enough to bring out the shapeliness of her hips". The message she communicates is cruelly contradictory - she announces unavailability while at the same time being provocative. Winston hates Julia "because she (is) young and pretty and sexless, because he want(s) to go to bed with her and would never do so, because round her sweep supple waist, which seem(s) to ask you to encircle it with your arm, there (is) only the odious scarlet sash, aggressive symbol of chastity".
Winston also hates Julia because she seems dangerous to him. He "dislike(s) nearly all women, and especially the young and pretty ones...it (is) always the women, and above all the young ones, who (are) the most bigoted adherents of the Party...the amateur spies and nosers-out of unorthodoxy". Julia in particular seems even "more dangerous than most". She gives Winston "quick sidelong glance(s)" when she passes him in the corridor at work which "fill him with black terror". Winston is afraid that Julia might be an agent of the Thought Police (Part 1, Chapter 1).
To answer this question, take a look at the section of the chapter which describes the Two Minutes Hate. It is here that Winston encounters Julia (known as the dark-haired girl) and outlines the two reasons for his hatred towards her.
Firstly, Winston hates her because she embodies the clean-living, pure, and chaste ideals of the Party. This is shown clearly through the following lines:
It was because of the atmosphere of hockey-fields and cold baths and community hikes and general clean-mindedness which she managed to carry about with her.
In addition, Winston believes that girls are the most enthusiastic supporters of the Party. Given Winston's hatred for the Party, this sets him in opposition to Julia.
Secondly, Winston hates Julia because he thinks she might be a spy in the employment of the Thought Police. This poses a particular danger for Winston because he has already committed Thoughtcrime by admitting that he hates the Party. Julia, therefore, becomes a figure of Winston's hatred.