Things Teenagers Do That I Don't Understand

Use of Automatic Doors
I've seen this not only on my college campus but on the ones I've visited, too. I see kids go up to doors and, instead of taking 2 seconds to open them, they press the disabled access button. It would be totally justifiable if they were a.) carrying something so they couldn't use their hands or b.) actually disabled but most likely they're not.
Excessive Cell Phone Use
When I got to school I used to put my phone on airplane mode so nothing would make any sounds during class. Then I realized what a waste that was and I turned my phone off instead. I see students constantly on their phones during class time when they should be paying attention but I can't see what could be so exciting.
Smart Phones
Why do kids have smart phones? Do they run a business? Do they have a job so important that they need to be able to check their email any time, anywhere? More than likely, no. They're playing fruit ninja and checking their Facebook. The most exciting thing my phone can do is play tetris. I can't even take video.
Chewing Gum
I don't really see as many people chewing gum in college since I guessed it stopped being cool once it was allowed. High schoolers are crazy about gum. But why though? It's not like real food. The flavor lasts for maybe 15 minutes and then you have this wad of flavorless gunk that you have to chew. People constantly get in trouble for it in high school, and even though they were told to throw it away they'd pop another stick in. It doesn't even make any sense.
The Friend Zone
It's classic; boy and girl are friends, boy likes girl, girl wants to remain friends. Now some cases for the friend zone I understand but others I don't. If a girl hugs, kisses, cuddles, or otherwise acts in an affectionate way towards a boy, why are they surprised when he starts to like her? What the heck women, make up your mind.