I build liquid rocket engines, and their fuel refinement systems; in a manner thats totally legal for normal (US) civilians.

for instance, did you know that your house's natural gas line is usually ~80% (varies by municipality, lowest I've seen is 74%) methane by volume, and is actually shockingly easy to purify and pressurize into usable methane for a methalox cycle engine?

its even easier to make LOX (liquid oxygen), all you need is: air (in vast supply here on lovely Terra) literally any cooler design that gets down to -183C....( the Glifford McMahon cycle works; and you can build that at home), a fractionating column, (you can buy them off the internet, you'll want metal, but glassware is still fine-ish as long as you account for thermal shrinkage....and never ever let it heat back up to room temp), a cryo-rated compressor (sold on ebay), and a dewar (also on eBay)?

I’m an incredibly good riichi mahjong teacher! I also teach go, shogi, and koi-koi too. It’s nice landing gigs when an anime convention pays me to go out and run panels about this stuff, helps round out the monthly income nicely, plus I get to travel and take good art pictures while I’m out!

Sorry, I'm a generalist.

I know a lot of things but none of them are relevant or impressive to anyone.

I mostly just get pushback when I try to talk about them, like I work in IT security, but apparently since I don't work for the CIA I 'must not be very good at it'.

I'm told almost every week that I'm excellent at teaching archery to complete beginners. Young, old, missing an arm, don't care, I'm always profusely thanked.

I'm a mile wide and an inch deep, baby.

not an expert per se, but i am very good at identifying manzanita species. Manzanitas are a genus of shrubs and small trees in the blueberry family mainly found in Western North America, especially California. There are a little over 100 species and subspecies, and the visual differences are often subtle. Many botanists in California don't even bother trying to ID them.

I am not a botanist, but i can reliably ID most NorCal, Sierra Nevada, and central coast varieties from memory, and with a key handy i feel confident i could ID any manzanita plant to currently accepted species or subspecies in person or with sufficiently detailed photos and gps.

The most striking feature of manzanitas is their bright red, smooth bark. They are locally called "refrigerator bushes" or "refrigerator trees" when large because even in the heat of summer the bark is always cool to the touch

Idk if I'd go as far as an "expert", but I listen to an obscene amount of thrash metal, and plenty of other extreme metal genres. I'm also a moderator for the !thrashmetal@lemmy.world and !heavymetal@lemmy.world communities where myself and a few others used to post daily for a couple years, no repeats.

I train and deploy search and rescue dogs.

I've shit my own pants more times than anyone I know

Data systems engineering! It started when MS pushed Windows 10 on me and my ancient laptop couldn't take it... So I downloaded a gnu/Linux distro and developed a CS hobby. That turned into a career and here we are : ) Thank you Microsoft

I am the lone expert at putting my underwear on myself as I have yet to see anyone else put my underwear on me. And if they tried, I’d wiggle so I could keep the top spot.

Repairing espresso machines. I've reached the point where I modify them and the parts can come from whatever is laying around. I'm pretty sure I'm done with it though, it's boring after doing something for over a decade.

You'll have to be the judge of whether it's niche or not, but my Japanese language proficiency - both output (speaking and writing) and input (listening and reading) - is in many aspects and contexts indistinguishable from that of native speakers. I started studying Japanese at the age of 15 - some 23 years ago. My first languages are Swedish and Hungarian. While I don't practice them myself any longer, I can teach the shamisen and the koto (Japanese classical instruments). Feedback from any and all pupils in any and all subjects that I have ever taught have been great, but I was aiming for something niche here.

Indeed, you are. I found your YouTube channel.

I really want to tell you, but the niche is so narrow, it would be difficult to reveal it without doxing myself.

So I'll just say that I'm probably top 20-25 in the world at playing a mod for a dead video game.

Not an expert, but I used to religiously and obsessively play the niche sport of Gaelic/American handball, specifically the 4-wall variation.

It's essentially racquetball, but with a much smaller, much harder ball, played only with gloved hands (gloves do not pad hands, just used to keep the ball dry).

Technically the 1-wall variation might have been the first ball sport to ever exist and is certainly the predecessor to modern tennis.

Awesome game, insane workout, and one of the few sports that is truly ambidextrous (handball absolutely requires use of both hands/arms).

I had to step away when I got into the tech sector and needed to dedicate most of my time to studying and working, but I played like it was a job for 8 years. Loved it.

Full English breakfasts.

I'm open to offers to speak at conferences. I can probably cover a full Scottish as well, but English is where my knowledge is deeper.

There was a game in the early 2000s that my family and I liked to play called Scene It. It was a DVD with accompanying board game - pretty cool. We had both a Disney and a Music one. I don't know if my music trivia still holds up, but I was an absolute champ at that game. I'd beat my parents hand over fist despite them being alive for a lot more of the events the trivia asked about.

In a similar vein, I am incredible at the Jackbox game Fibbage. On both sides, the trivia and the lying and suckering people in >:B

Modding Bethesda's Gamebryo engine games, especially Fallout 3 and Fallout: New Vegas, and especially doing so using only the built-in functions, i.e. no FOSE/NVSE. Not that I'm averse to using them, but I prefer to do what I can without them before I do. Thanks to that approach I had little trouble making Fallout 4 mods that could run on console editions of the game.

Foremost expert is pretty vague. Here's a couple of the more unusual and rare things I'm an expert in. I'm going to define it as less than 10 people globally know more than I do. Less than 100,000 people know anything beyond the absolute basics.

Applied plant breeding of cucurbits.

International marketing and sales of agricultural seed.

Map modding of ThinkTanks a 2004 game by Bravetree.
https://www.planetthinktanks2.com/forums/viewtopic.php?t=5544

Im one of those people who feels I kinda suck at everything but im very accomplished academically. I am an adminral in starfleet and a dashar master in the kdf so there is that.

Learning from others mistakes.

TF2 clip-making is considered "niche" now? Where did all the time go?
People don't make videos with SFM or Garry's Mod anymore? Really?
What about Skidbiti Toilet? Is that no longer a thing?

Nuanced thought.

My personal history and achievements. Glorious deeds and some other ones that made me infamous is the narrow circle of my fans.