I slow down, let them start to pass, then hit the gas so they can't pass
Usually my weapon of choice
If it's a 1-lane-each-direction road and they can't pass, I'll either brake check or just slow down below the speed limit alltogether. Keep in mind that I'm usually at least 5 over the limit, so if someone's tailgating me, they're even more of a dumbass than I am. The road that leads to my house is a 40mph zone, and I usually do at least 45, but if someone's tailgating me, I've been known to slow down to 30.
Usually my weapon of choice