One I adapted from the McGill women’s cross country team: “If unicycling were easy it’d be called ‘your mother’” 
that just became my facebook status
That one originated on the 1998 California Mountain Unicycle Weekend T-shirt. If you dig around you’ll find a discussion where I was looking for help on the last line. In the end, it came from my boss at Intel, a non-unicyclist but a professional technical writer. 
The last unicycle I bought has gears, brakes, a handlebar, and, potentially, more problems (more stuff to break). 
This thread would be a good place to collect the quotes that don’t fit in that other thread, the one about quotes from non-riders…
A couple of my uni quotes I came up with for t-shirts: 
http://unicyclist.com/forums/showpost.php?p=1055674&postcount=1
(<<< Check out my post count…just one to go!)
The beauty of riding a unicycle is that the rider becomes one with the
wheel.
It is a delicate ballet that is like skating and flying and you are always
on the edge of failure as you ride the line of success.
Whether tis nobler in the minds of men to mount their unicycles standing or
running, to take arms against a sea of asphalt and gravity, and by opposing,
end them.
Hahaha, that is totally awesome! I love this quote. Another good one is “We’re both one half on an entry” when asked if my brother and I were in a bike race. 