Hey.
the text greeting form of "hey" when someones pissed off.

The period at the end usually means you're in trouble.

Hey. is usually followed by:

"we need to talk"

or "stop using my bath sponge to wash your dick, Craig, you country bumkin shitbag!!"
Bryana: Hey.

Craig: Heyaaa

Bryana: Hey.

Craig: Um...what's up?

Bryana: What do you think.