I see them all too often and I always want to know. Mostly, because
you are funny and clever (hello, Mr. Mott, et al!), I want to hear
your responses as to why they are doing this.
Aside: I used to see guys masturbating all the time, like a couple of
times a week, in all different parts of the world, on beaches and park
benches and in cars, usually in the mornings, but that hasn't happened
to me in a while. Sorry for the un-family-friendly aside. It was
related in my mind.
Now go with your mailbox-sitter-guy theories!