Im actually schocked! and slightly ticked off!

I'm taking an Education class. Because i plan to be an Art teacher.. So this is the introductory course and out professor asked us to send a test message to her through our school website thing to see if it was working. She didn't tell us what to say or anything so i looked around at everyone else's and they all said " hi everyone!" or " TESTING 1 2" etc.... so i figured it do something different because thats what i do and i posted a joke that Whitney told me . " Testing 1...2.... Why does Snoop Dog use an umbrella?.......Fo Drizzles!" and then Michelle sent one that said " what it is?" and i replyed with "what it ain't?" you know.. ha ha.. funny... but NOOOOOoooooooOOOoooooo i got a reply from the professor that said " Don't use slang!" and the next said " this is an inappropriate reply!" With EXCLAMATION POINTS!!!!!!!!!! <<<<<<< like i has cursed or said something dirty... or insulted her or someone else.Its not like there was a serious topic and i was making fun of it.. it was just a test message to see if the dang thing worked! I don't see the nessesity of propriety in that situation.