This is the height of wit! Staying between the lines shouldn't be hard to do. You just use your eyes, line the car up, and go in. If you don't get it quite right the first time, reverse out and try again. If you can't get it right at all, then don't just leave your car where it is. Turn around, drive back to the place you got it from, and return it. As a next step, rip up your driver's license, because you don't know how to drive!
Only children struggle to stay between the lines, as the clever author of this poster correctly points out. Children's coloring books are full of untidy scrawl, which pays no regard to where they're supposed to start or stop coloring in. Perhaps going to back to childhood and spending a little time with crayons would help bad parkers with their hand and eye coordination? It has to be worth a try, right?