Seymour Krelborn is that you?
Aircraft oxygen systems. Test both passenger and crew oxygen systems for a large aircraft manufacturer and I am FAA certified to service and repair oxygen systems on private aircraft. I was hoping getting the FAA cert would allow me to retire early from my current employer and make a nice part time income. But with only a couple jobs a month on average, that prospect has gone to the wayside.
Installing acoustical grid ceilings, walking on adjustable stilts.
The kind that adjust from 24" up to 40"and are used by painters, metal stud framers, sheetrock hangers, ceiling mechanics (see above) and various other construction trades.
I can walk up and down stairs, climb ladders, and walk on uneven/rough ground. (even in the dark, with a pretty good buzz on! 
)
I am not an expert in anything.
“expert” is a strong word for me at my tender age and relative inexperience
I’m an expert of the geography of Milwaukee county, including bike trails, parks, woods, and secret areas. If ever you need a tour of Milwaukee… I’m your fellerina. Unlike many many age I have no desire to ever move from my hometown (at least, not permanently).
As part of my buisness I do antique restorations. For the specific category I concentrate on, I would put my ability and skills alongside anybody in the world. I’ve had people bring me a pile of parts in a box.
My buisness partner took over his grandfathers’ shop 25 years ago and is truly a master craftsman. There are 2 other shops within 100 miles that do what he does, when they no quote a job they give out his number. His humility is a hell of a thing to see. I’ve seen him do things that made my jaw drop, but he will always say Grandpa could have done it better or faster.
Oh and I can open a beer can really well.
Not in California you aren’t. That’s my territory.
US Clean Water Act consultant; expert in characterization and restoration of wetlands.
I’m an expert backer-upper, imo.
I spent years working as a yard hostler for a freight company. As drivers arrived, I took their rigs (18-wheelers) and backed them in. Also fetched and assembled the doubles rigs and brought them to the front for the drivers. I spent more time in reverse than forward.
Continuing brag; Over the years I’ve owned and pulled several tandem RV setups (usually Truck->Fifth-wheel->boat), and actually can back an entire rig into a spot if necessary. Our longest one was ~70 feet with 12 wheels on the ground. The wife and kids loved boating and skiing so I pulled these monstrosities to get us to out-of-the-way, unpopulated spots. Ski all day, then flip on the generator and retire to glorious AC. 
If you rewind a decade or two, I might have been considered an expert waterskiier, depending on your viewpoint. On a good day, I could run the buoy course, and I got good enough at barefoot skiing to do deepwater starts. (not me, but a pretty good vid of what it’s like).
At my job I have a good “working knowledge” in many disciplines related to electrical/electronics systems, and I do not consider myself an expert in anything. In any specific discipline, there are many people who know way more than me. But… the people I work for think I am an expert on all things electronic, which I find humorous.
I think that is generally the case but there are some fields in which a PhD is not the terminal degree. Classical musicians, for instance, often are considered expert with an MA. Are there any other disciplines in which you can be given life tenure to teach, for instance, without a PhD? I’m thinking some other arts might be the same. Creative writing, other pure arts rather than academic fields?
Cool, who won?
“Expertise in one field does not carry over into other fields. But experts often think so. The narrower their field of knowledge the more likely they are to think so.”* — Robert Heinlein*
Cool.
I use to service LOX on an aircraft that had 10 liters for the crew and passengers plus 25 liters for burn patients. This was on the C-9A which were the US Air Force’s version of the DC-9-30.
All the other aircraft that I worked on had gaseous oxygen systems.
Videogame design.
I’m the guy who gets assigned to your project when it’s royally fucked.
I am in the top tier at my hospital for hard IV starts, and I am the undisputed master at finessing kids through painful or scary experiences.
I am/was an expert in illegal narcotics use and trafficking investigations. Superior Court in my state said so. Doesn’t really mean much other than I could express an opinion from the witness stand. Normally, opinions are not allowed.
So you’re working on The Last Guardian?
Nicholas Pert (in 1998)
I have described myself as an expert at C and C++ in a resume accepted by a company that tested my expertise. I got the job. So, I suppose that counts. But, we really don’t have universally accepted credentials in CS. My degrees aren’t even in the field, for goodness’ sake.
But, I can teach good database design and object oriented programming well enough that my students understand the subjects well enough to land jobs. Maybe that makes me a better teacher than an expert, but still, it is useful.
Otherwise, I am a ‘Jack of all Trades’ and proud to be that.
I am reminded of a Heinlein quote: