girl and sling her across a bridge. >> then there is what our experts call sins of omission, intentionally excludeing peers to hurt them. one favorite technique is not tag the name of friend on a photo. take a group photo on instagram. everybody likes look they have having a great time, right? all the teens are tagged except for one, a simple mistake, don't bet on it. >> not everyone in a group photo gets tagged. because sometimes you don't like the person in the group so you're just like, no, i ain't tagging you. >> so even when you're invited to a party in real life, you can still get kicked out of it on social media. >> for a lot of 13-year-olds, they really have one social group and if they are left out of that one group, that feels devastating. they also view it as all of nothing. you're popular, you're in, you're cool or you're nothing.