Underpants, PLEASE!

I know that some people feel that wearing underwear is optional. Every once in a while with tight pants, or a skirt with that fabric that shows EVERY line, it is arguably acceptable. BUT if you are a dude and wearing low slung pants, underwear is a MUST. Here is a simple test for determining when you need to wear undies:
1.) With any sort of movement could my no-no place be seen? Yes = Undies, No= your choice
2.) Have I worn these pants prior to now without a wash in between? Yes=Undies, No= your choice

These are the general guidelines I wish someone would tell the dude who was on the elevator with me at Mesa last night, who when he lifted his arms to put on his backpack revealed to the rest of us in the elevator his whole (unruly) bush. The horror could have been avoided if he'd just thrown on a pair of chonies...