Define You Only Live Once Meaning

example 1:
kelly: "so I might have just given an old man a bj for some cocaine.."
lori: "what the fuck! I thought you were gonna make better choices after setting the Lawson's cat on fire.."
kelly: "fuck it, you only live once.."

example 2:
dawson: "man, can you believe it, after 2 years of being together, amber goes out and cheats on me! then, to make it worse, she tries to defend herself by saying 'you only live once!'.. fuck her."
ken: "so not cool. what a fucking stupid whore."

You only live once is one of the strokes best songs.

Push your care, push your burdens aside
Erase everything inside and leave just one thing on your mind.
You only live once so just go fucking nuts! (Go!)
Live life hard
Live life hard
You only get one shot
So shoot!
With every breath you take you're dying
With every step we take we're falling apart
If we only had one chance we'd breathe
Let's take the chance right now and scream
You only live one life
For a very short time
So make every second divine
Go!
Live life hard
Live life hard
Are you still breathing?
It's your heart that's beating inside
That keeps us alive
And for the very first time
We're pushing aside (to surrender)
Everything that I see in my eyes
Except for the one thing on my mind
That I am alive
For the very first time!

man 1: I am not sure that skydiving was a good idea...
man 2: Come on man! You only live once!

(man 2 pushes man 1 off the plane)