What makes an antagonist creepy or off putting in a horror flick and how to do it yourself?
The constant gaze, unblinking and fully focused on it's prey. It is a stare that goes one step past eye contact to an assessment of the victim's very soul. This look tells them that there is no where you cannot see.
A confident and oppressive stance. How one holds themselves says a lot about that person. Standing in a way that makes you as large as possible, impose yourself upon your space and those around you. Make the focus of your body the intended target, they will know they have your attention and they will regret it.
How they speak or if they don't speak at all. The word usage leaves no openings and the tone is devoid of emotion. Messages can be conveyed but usually they are only fluff when considering your true intentions. Short and blunt or needlessly complicated with your motive hidden in your words can work; unresponsive is alos a very good way to put someone in an ackward unsure state.
Doing unexpected things that are outside the social norm. This can be anything really as long as it gets someone's attention. It is a small gesture, can be physical contact or otherwise. It is to state that you do as you please and there are no boundaries holding you back. Keep it classy though.
Placement is important. Use poorly lit areas or stand with light at your back so that your features are obscured. You are one with the darkness, make that fact known. Don't miss an opportunity to hide in plain sight. Don't stick around, slide in and out of scenes without a word or much motion. Leave them guessing if you are or aren't there at all times.
Pace. Take your time. You know more about the surroundings than your prey would think and it scares them. You don't need to rush due to ensuring they are in a place where there will be no rescue. Savor the hunt and leave your mark on the surrounds so they don't get a chance to regain their calm.
Never hesitate. Doubt for even a moment gives away your power. They need to know you are unflinching and will not stop till your job is done.
If you try these things in real life make sure not to take it too far lest someone be put at risk. Everyone enjoys a good joke but there is a fine line that can easily be overstepped.