What happens if I get rear-ended and the other driver's insurance blames me?

Get a police report filed at the scene - that's your strongest defense because rear-end accidents are almost always the following driver's fault legally, and an official report backs that up. If the other insurer tries to blame you anyway, provide your report along with photos of the damage (which should show impact to your rear) and stick to a simple, factual account of what happened. Don't accept blame or sign anything that admits fault, and consider having your own insurance company handle the claim since they have incentive to fight back against the other side's bogus claim.