A word for someone who you feel uncomfortable with

Solution 1:

I used to work alongside such a person. He was okay, and acted friendly enough but there was something about him which made me internally cringe whenever we exchanged words. Perhaps it was his excessive enthusiasm that I found most irritating, in any case I always had an excuse not to join him for a coffee.

There are some people you do not want to be alone with, and not necessarily because you fear for your personal safety but because they are unnerving, and you feel uneasy in their company.

Her unnerving habit of touching people she was speaking to

uneasy: awkward or unsure in manner; uneasy with strangers.

Solution 2:

unsettling : having the effect of upsetting, disturbing, or discomposing

A Google Books example:

What I mean is, what do you really know about him? I find him unsettling. He's creepy. That woman Justine is scared of him.

Solution 3:

FRENEMY. I hope that helps :)