I thought this might be fun and interesting.
There’s of course Unicyclist, and then monocyclist?
Well if you’ve heard some others post em up, or make up your own.
I think Crotch Hoppers is a good one.
Made-up names for the activity: uniwheeler, one-wheeled cyclist, monopedaller, tantric cyclist 
Made-up names for the machine: PFB (permanently folded bike), PDDU (pre-dakoroman drive unicycle :D), yogic bicycle
Let’s expand this thread by telling us the names you’ve heard “non riders” use for us in passing. I’ll contribute (in the realm of MUNI):
Mountain Bike Unicycle (no kidding!)
and
One Wheeled Bike
Singlecycles/singlecyclists 
Some chav commented on my “unibike”. He seemed lost when I said to think about it.
Semibike/semicycle…
Semicyclist:D?
clowns!
I had a very young kid squeal, "It’s one of those CIRCUS RIDERS.
I do find it irritating how most people associate the unicycle with the circus. The circus is fun though, and I can’t juggle, or any of that stuff, but it feels so negative when people say it…
unibike, that’s great.
Same here when ever my parents friends see me there like “ are you going to runn off and join the circus ”
Also I get mad when I’m in the library and I’m looking at unis and people think its a joke
But hey, you don’t need other peoples acceptance, plus you always have the ability to change their minds. Just bust out a uni spin or do some grinds 
People don’t know what you can do
Eunuchs
It’ a one-legged bicycle.
dang, i was gonna say Tricyclist, but was too late
as mentioned in another post : “lost-a-wheeler” (rodomancat)
“Did you see the guy on that half-bike?” I got that today.
halfcycle! lol
eenwieler 
(in dutch:))
Heard someone call out, ‘Look at that one-wheeled penny farthing’