Best advice I have seen (frequently mentioned on ADV) for car tailgaters when you are on the motorbike is to weave about in your lane or stand up on the pegs.
I am frickin amazed at how well this works. I get this once or twice a week - commuting on a two lane road, no way to go fast or pass anyone yet I get some nimrod right on my ass. Standing on the pegs seems to completely freak them out as they all drop WAY back.
2004 R1150 GSA
2005 MV Agusta F41000S