Pettiness isn’t learned; it comes naturally. Ask any petty person why they’re like that and you’ll more than likely get a shoulder shrug in return. They don’t know. It’s not their fault they’re like this. Chances are they don’t care very much, either. That is until people get in their face about it. Then they’ll cut holes in all your socks, spit in your milk or do any number of the petty things on this list. Lucky number 13 is a personal favorite.