When:
You tell your friends to start working out so they can do parkour too.
Your shed is breaking apart and has no more paint at waist level.
You see a comment in this thread that says muscle up. Promptly look it up and run out to your shed in the rain and do it. (great technique, slippery surfaces will bow to me

)
You can be seen sizing up walls and ledges with lustful eyes while thinking "Next time."
One of your knees are down for the count at all times, but that doesn't stop you.