Feel free to hop in back and skip the fist bump. Simple way to indicate that you're just looking for transport.
"Hop in the front seat and greet your driver with a friendly fistbump"
It creates an expectation - and it feels like you're not really getting into the spirit of things if you're not playing along.
It's the whole reason I haven't tried Lyft yet too, much like other people in this thread.
I should mention, though, that you can have the healthy culture of driver respect at a place like Lyft with the professionalism of Uber. Sounds like the sweet spot to me.