why is it more acceptable to be cranky at 8am than 4pm?

i'm a morning person. my parents will both tell stories of a sullen teenager who, through high school and college, wouldn't emerge from her bedroom until 11am most weekends. but now, my internal clock has changed and i'm the one waking the rooster who needs to wake the farmers at dawn. and, i'm pretty pleasant in the morning. by the time i've showered and gotten out the door, i'm ready to have a polite conversation, even ready to have a few laughs.

come 4pm, i'm pretty tired. i've already been awake for 12 hours and accomplished most of what i need to for the day. i get a little cranky. sometimes edgy. a new acquaintance with a fantastic vocabulary has even called me snarky. i try not to subject others to it; i try to maintain composure, do what i need to do, and get myself home. but sometimes, just sometimes, it doesn't work. and i lose my cool. and people say, "why are you so cranky? does someone need a nap?" and i want to reply, "no, you jerk. i don't need a nap. but while you were being all nasty and sullen this morning until you had your 47th cup of coffee at 11am, i was running errands, conducting phone calls and being productive." no one would dare question that person about not being "on the ball" at 9am, but suddenly, when i'm tired at 4pm, it's a federal offense?

this is just one more example of ways that society is against early risers. first, there's no stores open for us to get errands done. then, we don't do things like clean the apartment because the vacuum is too loud for the sleeping neighbors. so we can't go out, but we can't be productive at home, and to top it all off, it's a crime to be tired in the afternoon? sheesh.