Using a diaper to shade your eyes while driving isn’t technically illegal, but come on

Q. I drive home from work every day using the northbound I-5 freeway through Irvine. The sun is on the left and comes into the driver’s side window. I see people using road maps, shirts, menus, newspapers and diapers as a sunshade covering the driver’s side windows. This blocks the driver’s visibility to the left. Is this legal? I know it is not safe. I am next to them, and they don’t see me.Tinting front windows is illegal, and you can see through tinting.
Scot