Why do some guys have the fight or flight response around me?

I’m not dating them. They are acquaintances / know some sort of well.

guy number one: immediately seemed flustered around me/ messed up his words. Then calmed down when started speaking to me.

guy number two: had to meet me alone, seemed mega uncomfortable and said this shouldn’t take long should it. Then I noticed his hands were shaking. He seemed nervous. Then said at end ‘see you around soon.’

guy number three: this is my boss. seemed very annoyed with me on one occasion and looked nervous. I was feeling nervous this occasion. Then other times met him after this he looked mega happy smiling at me. When I saw him at first on these occasions he slowly said ‘hello’ smiling, saying hello in this kind of overly professional, posh tone. Don’t know if condescending or if he was flirting. After our chat ended he went ‘okaaaay then. All on board?’

Why do some guys have the fight or flight response around me?
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