1. Signing emails with a single letter.
You are not Zorro. You are not the only person whose name begins with "E" in your county, let alone the whole planet. Use your full name.
2. Signing emails "xx" instead of using a word (like "best") or squeezing a freaking "o" in there.
"xx" is code for "I'm too cool to be spending time emailing with you and will therefore end this note with the coldest sign-off I can think of xx F."
3. Not taking your backpack off on a crowded train car or bus.
If you stick your backpack between your legs, my face doesn't have to touch your backpack, and I don't have to spend this ride thinking about how I want to murder you/myself. Everyone wins!
4. Tagging people in pictures of your baby.
You know that nagging feeling in the back of your mind that maybe this qualifies as tagging spam? Listen to it.
5. Walking next to a stranger at the same pace.
This is the universal way to make someone you have never known and will never speak to dislike you.
6. Addressing someone with a term of endearment 30 seconds into meeting them.
This goes doubly true for calling them "bro" or "doll" or "love."
7. Talking loudly on your cell phone in the gym.
Especially if it's a hotel gym or small apartment building gym or a gym that HAS A SIGN ASKING YOU NOT TO TALK ON THE CELL PHONE.
8. Singing aloud at the gym.
Are you Child Beyoncé training to be Adult Beyoncé? No? Then please run on the treadmill with your mouth closed and no sound coming out of it.
9. Putting your yoga mat so close to someone else's that they can't do their yoga moves without bumping into you.
It's your fault you strolled into the class five minutes late. If there's nowhere for you to sit without your yoga mat overlapping with someone else's, wait for the next class.
10. Leaving your phone on the table during dinner.
Are you having the most intense "Words with Friends" game of your life? Are you expecting the results of a blood test? Oh, you just don't want to miss any Facebook updates as opposed to actually engaging in normal human conversation. I have news for you: Talking is a way of getting concentrated real-time Facebook updates from a single account.
11. Bringing your super-drunk friend to a party.
Bringing a friend to a party is OK. Bringing a friend who is going to throw up in the bathroom and then drink directly from your bottle of mouthwash isn't.
12. Expecting someone to clean up after you rather than just cleaning up after yourself.
It doesn't matter if cleaning people are on staff, you can bus your own tray or put your own gym towels in the hamper.
13. Throwing your recyclables in the trash.
It's 2014, and not caring about the environment went out with stirrup leggings. Recycle. It's right next to the trash. If you're not sure which items you are carrying are recyclable, ask an adult.
14. Inviting your friends to like your band/comedy/blog fan page.
We already do a lot to support you by suppressing our urge to tell you that your dreams are stupid. Don't make us publically support you on social media, too.
15. Going to the bathroom as soon as you get to a bar or restaurant when you're meeting another person.
Especially when you're running late and the person you're meeting has been scrolling through their Facebook feed and texting people they don't care about for the last 20 minutes.
16. Holding your phone up at concerts to take pictures.
Even though no one behind you can see and your pictures are terrible and no one will actually want to see them when you force them to look at them.
17. Being late.
We can not stress this one enough.
This article originally appeared on Cosmopolitan.com. Minor changes have been implemented by Cosmo.ph editors.