I line them up on the dashboard. They're a marvellous conversation piece when I pick up prostitutes and/or female hitch hikers on lonely roads in the middle of the night.
I always use the daily commute for a rumage, roll and flick.
If the mrs knew how many bogeys she was treading on when she gets in the car at the weekend she'd be horrified.
If the window is open then out it goes, otherwise it's got to be the passenger footwell. Obviously you get the occasional bogey that can't be flicked and has to get wiped under the passenger seat.