The adjective blithe used to mean happy and carefree, but over time it's acquired a new understanding of someone who isn't paying attention the way they should.
If you have a blithe disregard for authority, you might just smile vaguely when a teacher is yelling at you to continue writing on the lockers with a Sharpie. If you're dancing to music while driving, and pass blithely through a red light, chances are you will be pulled over and given either a ticket or a talking to.
