A man pulling boogers from his nose, then wiping them on the train seat.
A young man pouring the remains of his drink into a mailbox.
More litterers than I can count.
And last and most gross, when I went into a bathroom stall today, the man in the next stall was pooping and eating a bag of chips simultaneously.
I would love to see robots or aliens conquer our species and force the survivors to behave.