If you're grown and calling people out for being 'fake' because you haven't seen a particular side to them, you probably have a lot more growing up to

do.
In my opinion, being fake is contradicting yourself or lying to someone for whatever motive and unless this side you're not familar with is completely and totally out of character, I don't see it being an issue of being "fake"
We're not cartoon characters that are to hold one persona and remain consistent with just that. Different people bring out different sides to us, just like different experiences form different reactions.

It's like witnessing your quietest friend screaming during a fire? Lol Every circumstance brings out different sides to us. Tying people down when they're exploring more sides to themselves, by stamping them with the label 'fake' is dumb.