When people are all of a sudden standofish/unfriendly to you but were friendly before

[La Trese]

I never understood whats the deal with this. Have you ever met someone, hit it off and they seemed super friendly to you. They add you on social media, comment and like almost all your statuses, so since its them starting it you think "hey they seem cool" and start to reciprocate and then all of a sudden they stop liking anything, you see them in person and they like actively avoid you more than once? What gives with that? I was wondering about this because when I was trying to make new friends in grad school, sometimes people would do this to me. So I would be like oooookay fine and back off and stop acknowledging them too and then literally yesterday I re met a few of those people through friends and they acted SOOOO friendly again and I was like wtf do you not remember ACTIVELY AVOIDING ME at the beginning of the year ooor whats the deal. Ugh people lol I literally would like to know what is the psychology behind this. Do people chase people who give "I don't care" chill vibes and run away from people who seem friendly or what gives?

[SerenityNoww]

Its hard to comment about the social media aspect of it, but as far as in person I've witnessed many times how certain people will talk and interact with me under certain conditions, but then maybe outside of work, or if they are with other people later on, they blow me off, as if they dont want to be seen associating with me.