How to show someone you feel uncomfortable around them?

The best way to show someone that they make you feel uncomfortable is simply to tell them! By phrasing your discomfort in a polite way, while specifying what action of theirs makes you uncomfortable, you can help to stop the behavior. It's best to use "I" phrases instead of "you" phrases to have a less accusatory tone (ex: "I feel unsafe" instead of "you are dangerous"). An example would be: "Excuse me, (name), it makes me uncomfortable when you get so close to me. I feel like my boundaries have been crossed, and I don't really feel safe." Then, politely ask them to stop the behavior that brings discomfort.

As difficult as it is, being upfront and honest is probably the best way to go. If it is a particular behavior that makes you uncomfortable talking to the person in a calm environment and explaining your feelings is a way to express that. If the person makes you overall uncomfortable, perhaps telling the person you need to spend less time with them is better. Either way, explaining your feelings to the person and allowing them the chance to change is probably the most fair solution.

I agree with others here who have said that being direct is the best approach. If someone is making you feel uncomfortable, even at work or school, there are things you can do about it. At work you can talk with the human resources department or an overhead manager about the behavior that is making you uncomfortable. At school, you can talk with the school counselor, principal, headmaster, or dean (depending which school level you are in). If it is someone you know personally and they make you uncomfortable regularly, try talking to them about the behavior. Start sentences with, "It makes me feel uncomfortable when you..." It is likely that the other person is unaware that you feel uncomfortable. As far as showing that discomfort, a lot of things come across in body language. Things like leaning away from the other person, refusing to make eye contact, refusing to talk to them or respond in a normal way, are all things that might tip them off that something is wrong.

If you are in the presence of someone who makes you uncomfortable, being in tune with your emotions and the physical sensations in your body will give you the much-needed insight into why you feel this way. You might be afraid to speak up if someone is doing something that makes you uncomfortable. Keep in mind that they may not know how you feel. Revealing your thoughts and feelings can smooth the way to better communication, negotiation and compromise. There will be people who are unable to take social cues from others and they make most people uncomfortable. If you have already tried other approaches in an attempt to be polite, limit your time with this person or walk away if necessary. I hope this helps you and anyone else in this situation. :)

The most effective way -from a personal experience- is, first, to blatantly keep a distance from them anytime you feel uncomfortable around them. If they continue, be open to them. Don’t feel ashamed or embarrassed. Tell them to keep their distance and that you would like them to stop what they are doing. In case they still continue, find someone to turn to. It could a teacher/professor, a police officer, your boss, anyone. Also, if your location doesn’t allow you to find a police officer, to make a phone call to ask help in case of emergency, etc. turn to a friend or acquaintance. Ask them to stay with you and talk. You don’t need to tell them what’s going on if you don’t want to. Just keep them close to you until the person that bothers you go away. Good luck and keep safe ;)

You can excuse yourself when they are around, or just don't hangout much with them.

walk away, do not be in a situation with them make your excuses and leave them to it they will soon get it