Without further ado, I give you The Stuff I Never Intend to Learn:
The difference between lie and lay
It has gotten to the point where, if someone tries to tell me about the difference between lie and lay, I will mentally shut down. I'd try to find a gif that appropriately represented mentally shutting down, except -- too late! -- I started thinking about the difference between lie and lay and now I can't do anything else but move on.
How to use "whom"
I've got a gut instinct for that one, and since no one ever died over the misuse of "whom," I feel like that's good enough for government work.
Plural/singular verbs in reference to groups of people
Is it, "The Jazz are 3-0 on the road" or "The Jazz is 3-0 on the road"? Does it make it worse if I use The Clippers? Either way, I plan to use the one that sounds better for the rest of my days, no matter what anyone tells me.
Anything involving the Eleventh Amendment
Wikipedia would lead you to believe that the concept of state sovereign immunity is a simple one. But it isn't, and now that I'm out of law school, I have no intention of even pretending I know what's going on there.
Bonus category: Something that I, strangely, care very much about
Differentiation between levels of formality of dress
To be fair, I often go to work dressed like a hobo and scare the bajeebers out of all my coworkers. On days where I am dressed like a hobo AND fail to do my hair? It's like the troll from all those fairy tales wandered out from underneath her bridge. So feel free to take this one with a grain of salt:
Black tie -- formal -- cocktail/semi-formal -- business -- business casual -- casual
This is the hierarchy of formal dressing. It is relatively simple to understand. If you are confused about any given outfit or event, just think about the hierarchy and try to decide where it would belong. However, do not try to wedge "Sunday best" into the hierarchy. It doesn't fit unless you're an elderly Episcopalian.*
If you are going to specify that you're holding an event where the dress code is Whatever, and someone asks you, "Hey, what does Whatever mean?", do not reply with, "Meh. It's not really important."
First of all, it is important. Second of all, if you don't care (which is different than something not being important), then you never should have specified.
And remember: Just because you're successfully in formal wear, doesn't mean you aren't also a sloppy mess. Take a look at some of those Oscar pictures if you don't believe me.
* For anyone who intends to dispute my assertion that Sunday best does not belong on the hierarchy, take a good, long look at any given church event. Even the ones that remain steadfast on the NO CASUAL WEAR TO CHURCH front fail to establish a dress code that makes sense. Typical male LDS Sunday best fits somewhere around (baggy) business, typical female LDS Sunday best can range from cocktail/semi-formal (yes, I know some would dispute that those are the same category, but I'm right), skipping business, and moving all the way down to casual (denim jumpers, anyone?)
Hence, Sunday best is a strange little concept all its own.