When DC were young, we lived overseas for DH's work (think military base) in a small housing cluster of about 6 houses. We knew the other families/couples well and there were always people coming and going (gardeners, drivers, maintenance staff) and there were always 2 guards on duty. Everyone was lovely and kind, especially with the kids.
One day, a maintenance team of 2 women and 1 man came to test the water cleanliness, they had to take samples from each house. When the man came near me, my whole body just went rigid and felt like I was turning to stone. He was smiling and chatting with my young DC who was standing near me, but I remember feeling sheer disgust at his presence. His female colleagues were absolutely fine.
After they left, I told DH about the man and said that under no circumstances was he to be unsupervised ever on the estate. The same team came back 3 or 4 times over the course of the year, and every time I felt dreadful and disgust at this man, and made sure DC were inside away from him.
The last time they came, it was just the women. I didn't want to I ask about the man, but I always got the feeling that they recognised and understood my intense dislike of him.
I still can't explain what it was: he was chatty and friendly, but it felt like a warning siren was blaring in my body when he was there.