to say 'YOLNT' is to say 'you only live nine times' therefore the person is referring to one's self as a cat.
girl: 'you sneaking out with me on friday to go to that concert?'
friend: 'omg no! we'll get caught for sure!'
girl: 'who cares if we get caught! YOLO!'
friend: 'mmm fine. YOLNT anyway. shout me a ticket?'