I filter a lot, and have "touched" somebody's mirror on a few occasions. In a year it might have happed 3 or 4 times. If this happens to you, how guilty do you feel? What do you do? On the one hand I feel like filtering is only acceptable if you don't bother anyone else while doing it, and that means never making the car drivers feel they risk damage to their car. On the other hand I think light contact is no different to what happens in car parks every day, and no damage should mean no drama.