You pocket dial.

While you’re busy surfing through the photos the bartender took, pointing out the funny faces of the girl you just met, you accidentally go to your recent calls and hit “Mom” or “Dad” with your finger as you place your phone back in your pocket or purse and guess what..??!!  You have no idea that you actually did this, but will certainly find out the next day when your parents tell you about all the yelling you did and all cackling in the background.