Growing up, my parents started taking the family to a movie on Halloween and leaving a big bowl of candy out with a note about just taking one, leave some for others, etc. Without fail, the bowl would be empty when we'd return ~2 hours later.
The first douche bag teenager with a pillow case and no costume undoubtedly emptied the whole thing and ensured the littles in actual costumes got nothing when they came by. That enraged me (and still pisses me off). F*ck those assholes. I begged my parents to let me dress up as a scarecrow, sit limp in a chair on the porch, and wait for the first kid to try to empty the whole bowl so I could traumatize him. Alas, they never let me do it.
Regardless, any teenager who shows up at my door without a costume or younger siblings in tow is getting handed one piece of the smallest/crappiest candy in my bowl, and invited to GTFO my property. And I'd be a lot meaner than that were it socially acceptable to do so.
