Sorry if this has been done before, couldn’t find one using the search function.
I’ll start:
You know you’ve had a good ride when:
The mud on your MUni is still wet the next morning
Your MUni is heavier after the ride because of all the mud.
…when you have to ride twenty miles back to your house with a broken bone.
a faucet of sweat is pouring on your face from your helmet…
…you come home in a better mood than you left in.
You’re exhausted, drenched in sweat, with a dozen new scrapes and bruises, but still stoked from your ride.
as long as i’ve had fun, it was a good ride!
When you join the navy and move to Maryland. 
that was the best unicycle ride ever.
…when you feel crippled, you feel like you’re going to die, your shin guards didn’t help at all but you can’t wait to get back out.
… you get home to find you only have one wheel.
oh… wait…
…You decide to wash your unis.
you finally land that new trick you’ve been working on.
… you leave a $20 tip?
…you are still motivated after hours of riding and do not want to stop;)
Wow, do you consider that a good ride!?! I would’ve put that in a “You know you’ve had a bad ride when…” thread, not here! 
when you come back with a non-broke uni
on the complete return leg of a 5 mile out and back muni ride you see that the only tire that’s been on the trail is yours
…you start calling your unicycle the Apollo Rocket of Love.
I like this thread idea; not sure if it’s been done before.
First one that came to mind for me: When you take a deep breath afterward, it makes you cough.
Or, when your legs are the most sore on the third day afterward!
Good one! I’ve definitely had that happen.
How about this: If you only notice how tired your legs are when you get off and find that you can barely walk.
when you take off your leg armor and can srape a thick layer of dead skin of each leg