Oh Yeah? is a verbal return to an action or more likely the oral depiction of an action (that may or may not have happened) to which the author of this phrase does not like. This is usually quite a startling way of saying "Over my dead body". Oh yeah? is 'most always followed by physical violence and expletives galore.
Traffic cop: Sir, I'm going to have to tow your car, you parked in the disabled space for two minutes.
Gumba: Oh yeah? Here's a better idea, you goddam little ratbastard!
*sound of nose being broken*