In most countries spitting on someone or something like a "wet willy" is both assault and battery. You only have to do a brief search of laws and court rulings to confirm this.

Assault is the fear you suffer by the action of such a clear vile act and battery is the contact made by the spit upon your person. Given that spitting at you is not a friendly act it must be deemed as an act of intent to harm, which is clear assault, followed by the spit touching you, which is battery. In the momment, you have the absolute right to defend yourself with physical force.

I can't think of a single country on Earth where a person does not have the legal right to physically defend themselves when another person, without justification or consent, physically assaults and batters them. The only thing that differs between nations in a situation like this is whether or not you are allowed to respond with lethal force.

^{It is important to remember that self defense and tracking someone down minutes later to retaliate are very different things.}