You can go to jail for assault if you pepper spray someone just to pepper spray them.
However if the person was pepper sprayed for self defense to prevent them from attacking or harming you then you will not go to jail for protecting yourself by pepper spraying them.
Some places may make it illegal to possess pepper spray so check with your local laws and regulations or they may have an age restriction on the pepper spray purchases or carrying or use of pepper spray.
But in most places it's legal to carry and use pepper spray in self defense.
Just don't spray someone with pepper spray just because you want too or if they call you names etc.
Only pepper spray someone as a last resort and only if they are trying to harm you or attack you.
Your first option though should be to get away from the attacker if possible but if not then pepper spray them to disable them.