Guy acting cold with me?

There's this guy from work that is extremely loud, confident, and funny around everyone, both male and female. He's a big joker that seems to be the most outgoing guy there. However, with me and with me ONLY, he acts terribly cold and dismissive. He can hardly hold eye contact and always seems to be trying to get away from me when he can. When we do talk, he keeps it as brief as possible and his voice goes rather quiet and serious, nothing like his normal self.

Why is he acting like that around me when he doesn't even know who I am?
Guy acting cold with me?
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