I'm in the US and a frequent Uber users, and I've only tipped once over 10 years. My rating is 4.93, so I don't think the drivers see me as an asshole.
It is possible there exists a table called dbo.user_ratings with a boolean column called IsAsshole, and you might have tons of rows there all with a 1 on the boolean column but the Uber APIs don't return that value. CEO Travis could tell us if it exists