YOLO means "You Only Live Once". It is an excuse to do unsafe or stupid things. It is very similar to the saying "What doesn't kill you makes you stronger!" (Which is a fabulous Kelly Clarkson song but a silly philosophy when it again comes to doing unsafe and stupid things.)
I make a point in my Health class to make fun of the phrase YOLO at any possible moment. "Yes, you should always wear a seatbelt and helmet, life isn't about YOLO"(and YOLO is always said in a demeaning tone). "But it isn't illegal if you don't get caught"...oh yeah...YOLO!!
I am very much on board with realizing you only live once and shouldn't let opportunities pass you by. Enjoy the sunset, stop and smell the lilacs, tell your mother you love her, hug a friend, call or write a relative, but don't do stupid things. Don't jump off a roof, don't try drugs, don't drive backwards down the street or be pulled on a skateboard behind a truck. Those things can kill you and you really are dumb to do them and yes, I am judgemental.
But then again, I do think that the concept of population control needs to be addressed through the law of survival of the fittest(or in this case the smartest), so I resend all of my judgement and demeaning ways. Go ahead do what you feel like, YOLO after all!!!