> (literally had an open bottle of wine under the handbrake)

Get out of the cab. Pay or don't pay, it doesn't matter. Note the cab number and call the taxi company or whatever organization polices the drivers internally (in Chicago, I think 3-1-1 is sufficient). YOU saw the infraction, who else do you expect will fix it? Sometimes the taxi driver will not see anyone else from the company, only the other driver who shares the car.