It's just stupid, and not a whole lot else.
YOLO is essentially carpe diem, but it's far worse. YOLO (You Only Live Once) implies that out of all of your days, you'll only truly live one time. These aren't sayings meant to be taken literally, and as such, "You Only Live Once" isn't accurate in the least. It's just an excuse for the younger generation to do stupid shit. Really, YOLO should be YLOO (You Live Only Once), in order to push the point that you only have one life in terms of mortality. YLOO doesn't really roll of the tongue though, does it?
Just seize the day, and don't use "YOLO" as an excuse to do anything.