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!!"
Craig: Um...what's up?
Bryana: What do you think.
Attractive girl to guy: "Go to hell, creep." (Moves to other side of bar.)
Alex: How the hell should I know?
Guy 1: Hey!!
Mystery guy: ::looks around confused::
Guy 1: O hi.