YOLO, short for "you only live once," is an Internet phrase that obtained a large following in late 2011 and early 2012. It used to be used to express appreciation of life's little things and opportunities, but has since been butchered by being used with any action or phrase.
"omfg lol just killed a homeless guy for another cardboard box #YOLO"
"lmfao i want to see if i can juggle soap in prison and get away with it!!!!11!1!1!!!1! #YOLO"