Oh that is SO frustrating!!!! My neighbour does that and seriously, I want to just floor it and back into them!
Is even more frustrating now my son has his L's and I cringe every time he has to back out.
Explain to them that your son is learning and he needs all the space he can get and you would hate for him to hit there car - Most people are pretty reasonable if you word it in a way that you are trying to protect them