No matter how much you disagree with a call, or how frustrated you get with a referee, it is a very bad idea to threaten or attack a referee. Referee abuse and assault are very serious offenses. USSF defines them as follows:
Policy Manual Section 531-9-3
(a)(i) Referee assault is an intentional act of physical violence at or upon a referee.
(b) Assault includes, but is not limited to the following acts committed upon a referee: hitting, kicking, punching, choking, spitting on, grabbing or bodily running into a referee; head butting; the act of kicking or throwing any object at a referee that could inflict injury; damaging the referee’s uniform or personal property, i.e. car, equipment, etc.
(4) (a) Referee abuse is a verbal statement or physical act not resulting in bodily contact which implies or threatens physical harm to a referee or the referee’s property or equipment.
(b) Abuse includes, but is not limited to the following acts committed upon a referee: using foul or abusive language toward a referee that implies or threatens physical harm; spewing any beverage on a referee’s personal property; or spitting at (but not on) the referee.
The penalties for abusing or assaulting a referee are stiff. If you abuse a referee, you will sit out at least the next three matches. As for assault, you can get suspended for three months for "minor or slight touching" of a ref, six months to five years for more aggressive assault. If an adult assaults a youth referee, the adult will get a minimum three year suspension. Not to mention, assault of a ref is a felony offense, meaning you could end up with criminal charges and jail time.
So keep your cool. We all get riled up at the ref from time to time, but when that happens to you, your best course of action is to keep your mouth shut and walk away.