The word of the day (albeit from Merriam-Webster, not Dictionary.com) is ‘hackles’.
Hackles are the hairs on the back of one’s neck. Dogs have them, and their hackles go up if they are frightened or angry. Humans have a similar response. I myself had a similar response, after getting up in the middle of the night to pee.
I have no idea why, but when I woke up, I felt deeply unsettled. I felt as though I was being watched, and the sensation left me deeply uneasy. I felt the hairs on my neck go up, in that classic fear response to… well, I don’t know. All I know is, something left me instinctively anxious, and this feeling did not abate as I went and washed my hands. It lingered, and my hairs remained at attention. My body was in fight-or-flight mode.
To raise someone’s hackles also means to make them mad. Pointing out someone’s mistakes – or having your own pointed out to you – can raise the hackles. It’s irritating and breeds annoyance, even if it’s justified. Putting someone on the defensive in an argument can also be considered ‘getting their hackles up’.