Picking one's teeth
Food has the tendency to get stuck between your teeth. That's why humanity invented toothpicks. And yet, it doesn't seem like the designers of toothpicks thought the whole experience through.
It's only natural to expect toothpicks to be found at the dining table. After all, that's usually the place where the food-getting-stuck-between-your-teeth happens. But actually picking one's teeth is not a presentable activity that you'd like to perform in front of other people.
You notice it has happened. "Oh, no!", you exclaim in your head. A little chunk of food residue clung itself to the interdental space. You find a collection of tiny wooden sticks that have been individually wrapped into paper packaging and placed into a container on the dining table. You grab one, unwrap it and start the annoying mission of removing the piece of food from your teeth. Your company appears to be unbothered by your nasty undertaking. The palm of your hand now acts as a shield from the looks of your friend, as your other hand starts to aimlessly pick at your teeth. It doesn't work at all. Also, you feel embarrassed by the activity. You stop and tell yourself "it'll come out eventually so I'll just ignore it for now". But you can't ignore it. It's too annoying!
You try to use your tongue to get the piece out, but also that doesn't work. Since the socially agreed upon technique of hand-shielding didn't prove successful, you excuse yourself, walk to the bathroom and pick at your teeth in front of a mirror. Let's just hope you'll be left alone and god forbid, your company doesn't walk in announced! But even in front of the mirror, you can't reach the damn piece! You're not even entirely sure about the exact whereabouts of the residue. Eventually, you surrender and promise yourself that next time, you'll bring dental floss.