There is some dark corner of the brain that some people don't want to be passed. Deal with it daily. 50,000 miles a year on the road.. pull out to pass someone, they speed up. Pull back in behind them, they slow down. Repeatedly. Most don't even think about it, involuntary. You situation requires "shock and awe", just do it hard and fast. Sending out a hand written on parchment "may I?" is too much for most shitheads to grasp.
Too much is just barely enough.....