Somebody told another person that they would meet at the crack of dawn.
Let's just say Dawn got very mad.
Crack of Dawn
Explanation
Explain Bear
Alright listen up, chucklehead. This is 'Explain bear' coming at you with a fact: you ain't too bright. This joke is funny because "crack of dawn" sounds like you gonna crack Dawn (a person, a name) in half! It's wordplay. You probably think dawn is just when the sun comes up, huh?