I'm Nigerian and get the same reaction to my "proper English" from time to time.
I don't trip though. Americans--white, black, yellow, etc-- are sometimes ignorant as hell! It's as though they subscribe to the following rule: IF IT DOESN'T AFFECT ME DIRECTLY AND IMMEDIATELY, THEN IT IS NONE OF MY CONCERN! I simply tell them Nigeria is a former British colony and ask if they've ever travelled overseas. The answer is usually NO; this gives me a chance to educate them further.
So where are all you NAIJA peeps headed this fall?
Can I get a head count?