I don't understand what the situation is you've set. Where are you, where is the car? What kind of intersection, two roads, a tee or something else?
I don't have the issue here your title seems to indicate. Are you sure it's a turn signal and not that they are flashing their parking lights and from your position you can't see the other flashing on the other side of the car?
Most people here that bug me at intersections are just trying to be nice. Some get mad when their generosity is refused.