AM and PM... How the hell am I 27 and only just understood this?

I'm writing a report at work and quote the time as 12.00am. My boss said I may want to change it to pm becasue 12am is midnight. WTF... I wake up at 6am... hours pass 7,8,9,10,11 and then 12am comes over. Apparently not, it magically becomes 12pm and then resets to 1pm. This is the biggest lode of shite I've ever heard (A quick google search supports my bosses view).

Not only has a part of me died inside, My respect for the world has decreased. How the hell did I get two degrees in Astrophysics without knowing this!