Back Off!
One of the most irritating feelings is to have somebody tailgating you. It goes beyond irritating when you're on a motorcycle.
Any need you may have to slow down suddenly becomes a life-threatening situation. You may get slowed down to avoid that deer, but the tailgating motorist runs you over. So how do you avoid it?
The first thing you should do is signal the tailgating motorist to give you more space. The signal is given by extending your arm downward and making a repeated rearward motion with the palm of your hand (starting by your body) as though you are literally "pushing" the car back. Most motorists will recognize and respect this request for more space.
If the tailgating motorist won't back off, the next best option will be to find a safe place to pull over, and let the tailgater pass you. Speeding up is not a good option, as it will probably just result in being tailgated at a higher speed.
Keep in mind, this goes both ways. If you tailgate an auto while riding a motorcycle, you're asking to join the occupants of the car via the rear window. You should keep a three second (or more) margin between your bike and the vehicle in front of you, just like the three second margin you hope exists between your rear tire and the front of the car following YOU.