I'm a professional driver, driving 45 ft long coach buses, and I get caught behind those folks frequently! And in a bus, passing them is often not an option (buses don't change lanes and accelerate as easily as cars, and in traffic, no one wants to let a bus over!).
Since buses aren't conducive to impatience, I've forced myself to just relax and wait until either the slowpoke makes a turn, or I reach a place where I CAN pass them. Any other approach really just adds to the overall road rage level...
In the grand scheme of things, being caught behind a slowpoke doesn't tend to last for more than a few minutes, and the actual time lost is considerably less than that, so I find a zen approach leaves me less exhausted at the end of my day!
Not to say I don't sometimes wish I could Taser them!!!
Cheers, Tim