What is the one thing in your life that you’re really, really good at, that serves simply to amuse you and has no practical value as far as employment, education, family, or otherwise bettering yourself?
I myself have many areas that I’m deficient in, but I wouldn’t be too surprised if I was one of the best Super Mario Bros. 3 players in the entire world.
I can do the trick where you tie a maraschino cherry stem into a knot in your mouth.
The record time used to be about 11 minutes, recently, someone found a way to beat it in under 3 minutes. That same person can also do it in about 50 minutes without using any warps.
How fast can you do it?
If I know the capacity of a sporting arena and can view the crowd attending an event, I can guess the number attending within +/- 5 percent.
Not that fast, probably. But I don’t go for speedruns, really. I like to delve into each level, get all the secrets, farm the 1-Ups on stages like 1-2 and 2-Fortress, and so on.
I love to travel, but speak no other languages.
However, that mangled, barely, English+Any Language, you hear wherever you go. Even if it comes down to charades and pointing. Turns out I’m naturally gifted at that!
I can make farting sounds with my hands. Most dogs go crazy when they hear it.
I have memorized Pi out to 100 decimal places.
Other than that, I have nothing.
But can you do this?
Reading upside down. Also, juggling. And making dashi holders out of the paper the chopsticks come in, although that smacks of useful. It still amuses me, though.
Burping at will. And bending the first joint of my left ring finger backwards, and bending the second forward without bending the first joint.
Creeps people out.
I have trained a chicken to perch on my arm.
I can twiddle my thumbs in opposite directions. Most people can’t - they twiddle them both in one direction, then in the other.
I’ve been driving people crazy with this for years. Everyone thinks they can do it, until they try. 
I can call spirits from the vasty deep.
I’m really, really good at “name that tune” with rock and roll, from the late 60s through today. Earlier rock, I have no idea. Any other genre, forget it.
But spin the dial and stop at each rock station and I can tell you the song and artist by the end of the song, if not in a few notes.
I have a knack for mimicking accents, and can do a reasonable variety on cue. It’s never been applicable to any job I’ve held or pursued, instead getting used in roleplaying to entertain myself and my friends. Every now and then, I consider trying to get into voice acting, but I’ve never followed up on it.
Why, so can I. Go figure.
I can do that! Can you do it with your arms?
Since you probably have a good shot at it, try this:
Put both hands flat on the table. Lift the ring finger of your left hand and the thumb of your right. Put them down. Now lift the middle finger of your left hand and the index of your right. Keep going. When you run out of fingers in one direction, switch. Then try it offset by two fingers (middle finger left and thumb right, etc.). Or try it ring finger to pinkie. I’ve only ever met one other person who could do this without struggling–one of my sisters.
I’m fast and pretty accurate rendering spoken language (including accents and nuances) as IPA and I can type it out in a word processor or post it in a vB message board post.
I can also tie a cherry stem with my tongue. Useful only in that it got me free drinks when I was younger and prettier.
Umm…I’m pretty good at fire poi. Not the best, but not a noob, either. That will probably only come in handy in the event of a zombie apocalypse, and only if zombies are flammable.
I’m really good at making that “trilling” sound - where you rest the tip of your tongue against the front of the roof of your mouth and vibrate it. I don’t speak Spanish or any other language that uses it for rs, but I can trill melodies and imitate purring.
Also, I can do the clover tongue. Hey, it impressed a lot of people back in 3rd grade!
ETA: Ooh, I’m also kind-sorta double jointed in my fingers - when I press them back, they form a 90 degree angle with my palm, and I can lock my thumbs behind my hands. I guess I’ve got an abundance of completely useless skills.