Wait until the last minute to cancel something (intentionally).
If you’re going to make the bitch move — and we’ve all done it — make it early and give that person a chance to re-plan. When you receive the text message a cool 30 minutes before you were set to do the thing, and you just know that the other person has been waiting to bail for hours, if not days, it is in the top 10 most unsatisfying feelings you can experience. You want to bitch them out, but you can’t really. You want to make replacement plans, but it’s too late. You want to throw your phone across the room, but then it would break and you have no money. It’s just awful.
Talk in gory detail about their sex life with someone you know.
Why do people do this? What stands to be gained from cornering you at a party and unloading the most intimate details of their sexual history with someone you know in a completely platonic, very real context? Do they not understand that you now have to see this person and feel your eyeballs sizzle with the pungent heat of their bedroom prowess?? It’s almost as if you’ve had sex with them yourself, but somehow even worse, and it will forever be weird.
Start things off by saying “I’ve heard so much about you!”
Ew, no, what did you hear. It was bad, right? It couldn’t have been good. Oh, God.
Deliberately wait for extended periods of time to text back, so as to assert power.
This is the human equivalent of peeing on a patch of land to mark your dominance, and it’s awful. Sometimes you’re really pressed, and you want to text with your crush, and you’re having a hard time creating that desirable air of mystery and suspense — the worst possible response to this is the other person taking their sweet time and being in no rush to communicate. It just reaffirms your already-intense suspicions that you come off as a sweaty slow loris, and you probably don’t deserve someone so cool.
Construct an elaborate lie that involves you.
There are few things more awkward than someone concocting a poisonous web of a story (often to get out of a social engagement, or to sound impressive, or both) and bringing someone else into the ethical hot mess. You just stand there uncomfortably, not wanting to trip any wires of their dishonesty, and basically become some horrible criminal accomplice so they can make their internship sound more glamorous. And your choices are either betray them and reveal the lie, or go along with it and risk being discovered. There is no good way out.
Not tell you when you have something wrong with your face.
Allow me to set the scene: You’re at a dinner with friends, hanging out, having a good time. You spend minutes, hours even, laughing and drinking wine and carrying on. You excuse yourself to the bathroom, and glance in the mirror, ready to see your predictably sexy, un-blemished face looking back, only to see that you have a very noticeable spot of sauce dotting your cheek or — God forgive us — a booger. Suddenly, you are overcome with shame, and in roll the devastating questions: How long? Who has seen this? How could my friends have betrayed me in such a way? Et tu, Steve? It’s cause to never leave that bathroom again, honestly.
Text “we need to talk.”
The Crown Prince of all mean things you can do to someone else, texting these four words with no further explanation taps into a level of pure cruelty. It’s like calling someone several times in the middle of the night, leaving no message, and not explaining it. People are going to assume the worst, and having to actually pick up that phone and find out what is going on is the kind of thing that otherwise-sane people will put off for days on end. They cannot get mad at you for not promptly responding to the scrawled-note-attached-to-a-brick of a text message that they just threw at just window, they know what they were doing. 
