I have one word: teenagers.
See, I can totally see doing something that stupid when I was a teenager, or seeing one of my friends do it back then. Hell, we did far stupider than that. But yeah, flinging some used gum up to a ceiling to see if it would stick? Totally a bored teenager kinda thing to do, and it doesn't automatically mean they were completely failures in life after that. Doesn't mean they weren't, of course, but doesn't mean they were.
Did I ever do that? Nope. Did I ever do stuff like that, or stuff worse, stupider, or more inconsiderate than that? Of course.
I was a teenager.
"The Customer Is Always Right...But The Bartender Decides Who Is Still A Customer."