I saw a post about a Uber driving wanting to give a bad rating to a pax for not tipping him. I'm a baby boomer and was raised that you tip based on service rendered. Getting a tip is a privilege not a right. There are a lot of reasons that you might not get a tip. Maybe they are new to the app. and didn't want to tip yet, maybe they just had enough to get the Uber, maybe they planned to tip when the got home and just forgot. maybe they just NEVER tip for their own reasons. Keep the karma good by giving them a rating based on what type of passenger they are. It all balances out in the end when good tippers are generous.