When people are driving in the fast lane and aren't moving (and darting around them isn't a viable or safe option), I accelerate right at the rear of their car and follow them closely. Most of the time, it works wonders because from the front, my car looks extremely convincing as a police car so they move out of my way long enough for me to pass (of course, then they see I'm a fake and then freak out). In the event that they're still too stupid to move, I'll follow them really closely hoping to make them uncomfortable enough to scoot over, otherwise I wait for a big enough gap in the slow lane to overtake them that way, pull in front of their car, and then give them a dosage of their own medicine (unless I'd be effectively holding up more cars behind them, then I don't do that) before going my own way.