Signs that a person does not like you are that the person makes no effort to spend time with you, does not remember what you say and doesn't make eye contact with you or smile during interactions with you. A person who doesn't like you also keeps body language closed when near you, and treats you the same, or worse, than others.
A person who doesn't like you does not take an interest in what you say. He is also happy to make decisions without your input. When a person likes someone else, he usually wants to learn about that person. If the person never initiates contact with you and he does not remember what you say, it's a sign that he does not like you.
A person who doesn't like a person refuses invitations to spend time with the person and keeps conversations with the person short and to the point. Although the person might have conflicts with specific occasions, a person who likes you finds time to spend with you. If the person claims that he has no time whatsoever to carve into his schedule for you, it's a sign that he doesn't like you.
Similarly, if the person keeps his body language closed when near you, such as folded arms, it's a sign that he doesn't like you. Another sign is if the person is slow to look up from his computer screen when you enter the room. The person might also have a shorter attention span when talking with you as compared to others. A person who doesn't like you also never gives you special attention. In fact, a person who doesn't like you gives you the same treatment as everyone else or even appears to have less time and attention for you.