"Tired" is an excuse that many
people use when they look like crap. Some are legitimately tired, but the amount that are using it as an honest excuse are dwindling.
People also use Tiredness when they are annoyed but
don't want to seem like total jackasses.
Friend 1: Dude, whatsup with you? You
look like crap.
Person: Can
you shut up?
Friend 1: What'
s wrong man?
Person: Sorry, i'm just tired.