High Quality Cayenne Pepper Spray.
Using pepper spray for female self defense, is done much the same way as in any other assault. The only difference is that you must first recognize what is happening, then verbally attempt to stop the man's behavior. Once you say "Stop!" in a forceful way and he doesn't comply you have every right to stop the continued aggressive behavior by using pepper spray  preferably, a high quality cayenne pepper spray.

For Female Self Defense
In this sort of situation you must also have the self defense spray available to you. Keep it nearby, particularly if you're with someone you don't know well. If you need to retrieve it from a purse or jacket pocket, rehearse a reason in advance. Otherwise you could find yourself unable to get to the defense spray when you need it.

When you shoot, again, do so quickly with surprise. Then, as with any other female self defense countermeasure, leave quickly. Don't stay with the date! If you must shoot the cayenne pepper spray in a car or other enclosed area get out as quickly as possible. Otherwise you'll be affected by the capsicum in your self defense spray.

Special Notes

In all cases of an attack from the rear you must know if there is a weapon involved! Don't spray the area in a panic. The assailant may be affected by the spray, but if he's close enough he may strike with the knife or shoot the gun.

A special note to women about rape attempts. If you are assaulted with a weapon, a gun or knife, at close range, keep in mind that, at some point, the rapist may be preoccupied with the rape itself. He may assume your fear will keep you in line. Let him continue thinking that. At the first opportunity get your pepper spray point it right at his face and keep spraying him. The capsicum in your cayenne pepper spray will disable him, so you can escape. JUST BECAUSE THE RAPIST DOESN'T HURT YOU INITIALLY DOESN'T MEAN HE WON'T LATER. HE MAY ATTEMPT TO SERIOUSLY HURT OR KILL YOU AFTER THE ACT ITSELF DON'T GIVE HIM THAT CHANCE!

Finally, keep in mind that an assailant that's hitting you may not have enough control to keep you from breaking free. If you can, break free at the first opportunity and use the spray. Also, if you feel at any time that the assailant isn't going to let you go or let you live, you must attempt to get away using your cayenne pepper spray, even if the assailant has a gun or a knife.