A facial expression produced by a person who doesn't know whether to smile or frown at a comment(possibly a racist or sexist joke) in case everyone else shuns him/her for the rest of the day.
man at party: why do women have breasts?"
(pause while people give attempts at answers)
man at party: so you have something to look at when you're talking to them!!!
(another brief pause)
one person listening to the joke smrowns and then checks what everyone else is doing and then does that.