(defendant (tractor operator) appealed jury verdict finding plaintiff (motorcyclist) was not contributorily negligent in a tractor/motorcycle accident in which plaintiff had been drinking alcohol; appellate court agreed prejudicial error occurred when jury instruction regarding the presumption of intoxication for criminal cases was given in a civil trial; error also occurred when plaintiff’s attorney flagrantly violated motion in limine by asking questions regarding lack of DUI prosecution for plaintiff and objections failed to remove the harmful effect of hearing the statements, so error also occurred by trial court’s abuse of discretion in failing to grant a mistrial; case remanded for new trial).