1. When one person asks how they look and the other replies a little too honestly instead of going with a trusty affirmation like “You look amazing!” Because even when it’s demanded, the truth can be seriously aggravating.
2. When either party imagines their partner having sex with someone else and the thought disgusts them so much that they either have to projectile vomit, or vent their frustration by picking a lover’s quarrel.
3. When your sex drives fall out of sync and one person desperately wants to get laid while the other just wants to curl up and go to sleep several days in a row.
4. When one person tries to motivate the other to start exercising or eating well because it’s good for their health, but the other person hears: “You look like shit so get to the gym already, Fat Ass.”
5. When someone brings their work problems home and the other wants to have a nice relaxing evening but it’s impossible because their partner won’t stop bitching about his or her colleagues and/or a frustrating project.
6. When your moods are so misaligned that one person’s happiness becomes the other’s poison. Grouch Master Flex and Happy Go Lucky do not get along.
7. When one person reflects too fondly on a particular incident that the other quickly realizes must have overlapped with a previous relationship and the idea that their significant other was ever at all happy without them drives them absolutely NUTS.
8. When the person reflecting on their past then dares to deny smiling while recounting the ex centric memory in question, which makes the whole thing yet more offensive.
9. When anyone’s ex comes back into the picture—because you bump into them on the street or because a text is received or a Facebook photo pops up—at a bad time (i.e. at any time ever).
10. When one person says or does something the other considers inappropriate in public or in front of mutual friends.
11. When you’re both 1,000 percent positive in your opposing accounts of a past event.
12. When one person’s 1,000 percent certainty is proven 1,000 percent wrong and they’re super touchy about it.
13. When you’re running obscenely late because one of you is having a wardrobe crisis and the other’s had to wait around for what seems like forever.
14. When you just can’t agree on who’s a bigger fan of [insert TV show and/or celebrity and/or band].
15. When a mysterious stain appears on the carpet, bathroom towels, or sheets and both of you are absolutely positive it’s not your fault.
16. When someone makes the mistake of citing the other’s menstrual cycle as the root cause of her behavior.
17. When one person feels they’ve been contributing more than their fair share to the general upkeep of the household and snaps as a result.
18. When someone makes a well-intentioned statement that’s wildly misinterpreted and there’s no way to reverse the damage done because Pandora’s box has already been opened, albeit by accident.
19. When one person’s family relation or good friend does something extremely annoying and the only reasonable thing to do is yell at each other even though doing so doesn’t help anyone at all.
20. When one person desperately wants pizza for dinner and the other insists on preparing a balanced, sensible meal that is entirely unsatisfying.
21. “You suck at folding!”…”You suck at life!”