Gross Personal Hygiene Stuff
Some things just shouldn't be done with other people around. Whether it is clipping your finger nails, q-tipping your ears, or tending to whatever gross things your body produces, no one wants to see that. The perfect time to tend to those sticky hygiene issues is while your car is sitting in traffic. If your fellow drivers happen to catch you fingers deep in a nostrill, that's on them. They should have kept their eyes on the road anyway.