Should I start with what being liable is?
How about the difference negligence and premeditation?
If you are intent on them running into the back of your car at speed, in your anticipation of the accident chances are you will tense every muscle in your body.. upon impact.. you will be hurt worse/more severely than the person caught unaware by your stupidity.
That being said.. there are several things you can do rather than get so upset you are contemplating attempted vehicular manslaughter...
You are apparently not in a hurry.. so you're not dumb. You can manage your time just fine.. so spend a few more minutes and screw with their head.
It's rather entertaining to condition someone as you drive. When they're on your ass slow down.. they will create distance or go around.. speed up when they create distance till they close the gap again.. slow down again.. speed up when there is distance.. see how long it takes them to realize that speed is increased with distance.. It's kind of fun actually.