how do i deal with someone who acts too familiar when i don't know them

Id try to chill about it.

They could be really insecure themselves and be overcompensating....or needy, or jist a narcissist trying to friend you up .
...its hard to tell.

Just relax....time will tell what drives this in them🤷‍♀️

Is it like asking too many personal questions, or getting too much into your personal space?
If they cant take a hint, then sometimes you have be blunt with the situation.

Could be a new best friend. :)