Not getting enough sleep. "But Anna," you ask, "How can I sleep when there are so many mistakes to make?!" Don't worry, you have an entire decade's worth of days and evenings to irrevocably fuck up your life. (1.5. Not washing the pillowcases often enough. Once a week, or else your skin will suffer.)
Wasting money on restaurant meals. I spent the first 5 years of my twenties dragging my hungover ass out of bed and feeding a $14 artisanal omelet to my mouth. If only I had skipped maybe one of these a week, I'd have $60 extra for grocery money, or for one GIANT artisanal omelet that we could all share.
Washing your hair too much. Yes, too much, especially if it's not stick-straight! By the time I was 24 my hair had the consistency of tree bark. Skip a few shampoos and just condition, or use dry shampoo! I use Rene Furturer, that stuff in the dark green spray bottle.
Being addicted to social media. He liked that picture of your cat on Facebook, and then you retweeted his tweet, and then you trolled all of his friends' Instagrams to try to find out if he was dating someone else, and then he posted a news article to your wall that related to this inside joke you guys have, and by the way, it is a beautiful day outside.
Spending all your time in a relationship. Friends of mine who were with the same guy all through their twenties are lamenting it now. Before you settle down, you gotta get some strange. To truly appreciate the good men, you have to road test the bad ones.
Or chasing after someone who is completely disinterested in you. Does he never ask you questions about yourself? Swoon. Does he take at least 24 hours to text you back? Nice. Are you in his phone as "Mike" so that the other girls he's hooking up with don't know? Yayyy! (No.)
Hooking up (the "feelings" way, not just the "casual" way) with a friend's sibling. If the sibling lives in the same town that you both do, this is the most awkward social decision you can possibly make, besides going to Jay-Z's 40/40 Club in a chicken suit or something.
Splurging on beauty products that you know in your heart you won't use. Sephora is in business because "If I just buy this $75 unicorn-horn face powder, everything in my life will immediately improve and I will know what the fuck I am doing" seems logical to us, briefly. It's not true!!
Hoard $15 H&M trend pieces instead of saving for something expensive and timeless. A cheapo peplum top (last year) or pleather leggings (2007)ish are always bound to go out of style, like, tomorrow.
Extreme diets. No matter how many lemon juice, cayenne pepper and holy water holistic cleanses you go on, you'll end up at your normal weight ultimately.
Drunk texting/dialing. And rolling over in the morning dreading to look at your phone. Hoooo boy do I know what that's like.
Get a long-term pet with a significant other. So you and your boyfriend decided to drop a few of your start-up paychecks on Chuckles the $1,200 cockapoo. If you don't last as a couple, Chuckles is a child of divorce, which we all know is a gateway to drugs and juvenile delinquency.
Getting sloppy with birth control. It is a joke to try to pretend that it doesn't feel better without a condom, but everyone's gotta. You gottttttta.
Being health-bipolar. During the day we're drinking green juice and going to yoga. At night we're out partying with friends and ending the night with 4 a.m. fast food. The former does not detract from the latter — your body is just confused as shit.