Ariana: I think Mikey is high..
Justin: Nah, she is having a Vietnam Flashback from when she was on Hannah Montana.
Selena: I get it. Disney is awful.
Ariana: Yeah, Nickelodeon is better.
When a person has a resting facial expression which is incredibly vacant and vaguely shocked. Suggesting the person is having a flashback to an experience had in the Vietnam War.