1. Throwing up, or even giving that weird “Oh God I’m going to throw up if you don’t stop talking to me” face while rocking backing and forth.
2. Saying the wrong name, especially the name of the ex you were trying to get over by going out to the bar in the first place.
3. Asking what their name is mid-sex, and not even trying to it in a classy way like “How do you spell your name again?” even though that would be a strange question to ask during sex.
4. Acknowledging the products they have in their bedroom/bathroom that clearly imply there is another person regularly getting some at this apartment.
5. Using the second toothbrush which most definitely belongs to someone else.
6. Realizing that you don’t have any protection and being so drunk/pressed that you start insisting to do things without any protection whatsoever. If you say the words “We’ll just get a morning-after pill,” you need to review your life and choices.
7. Trying too hard to talk about seeing each other again when they are clearly not interested in the least and are just trying to end things with some class.
8. Getting caught making too much noise when you’re trying to sneak out before the sun even rises.
9. Making comments about how this isn’t how your ex did things, or you’ve never seen that before, or how weird everything is.
10. Repeatedly insisting that you never do this, and that you are so embarrassed to be the kind of person who has one night stands (even though the person you’re with is clearly one of those people, too).
11. Messing up the sheets in some way.
12. Answering a phone call while still in their bed and telling your friend “I can’t talk right now, I’ll tell you about it later.”
13. Prying for information about whether or not they have slept with any of your friends.
14. Asking them how many times they just take people home after a night out, and aren’t they afraid of getting STDs?
15. Telling them that you “don’t kiss one night stands, because it’s just too weird and personal.”
16. Making it clear to them in explicit terms that you have no desire to see them again, and not at least maintaining the veil of politeness and courtesy.
17. Bringing Magnum condoms when that is clearly not what the situation requires.
18. Bringing up the fact that you really only went out because you’re trying to get over something really complicated, and you’re not sure if you’re completely over it yet.
19. Repeatedly talking about how drunk you are and how you can’t even really tell what they look like.
20. Lying about your name when you’re in the bar and then accidentally identifying yourself by your real name halfway through your encounter.
21. Falling in love with them over the course of one night, even though in the morning you are both leaving for opposite sides of the world and you know (even if you won’t admit it) that you will never see each other again. Above all, try not to do this. It won’t work out, even if you think it will.