Are there people who just give off vibes that make you uncomfortable but you can't explain what exactly it is about them that gives off those vibes?

Last summer my nieces came over to swim in the pool my apartment complex has. There was this lone older man who gave off vibes I didn't care for he just seemed creepy to me. He never did anything but there was just something about him that made me uncomfortable. The entire time my nieces enjoyed the pool I kept tabs on that man until he eventually left after awhile. I've only ever felt that exact feeling one other time at a park when I was a kid. My brother and I were playing at the park down the street from where we lived with our mother. I was always the shy one and was abandoned while he ran around with other kids. I hung back and noticed a lone man long hair in a ponytail rather scruffy looking potentially homeless. He just sat on the bench and watched the kids. Could have been harmless but his vibe I didn't trust it felt odd. I felt compelled to watch this man. Eventually I told my big brother I wanted to go home. I saw him a few times at that park and he did the same thing each time and each time I felt compelled to keep an eye on him.