For a celebrity with some experience on the internet and not a small amount of money, that's a pretty easy mistake to avoid.
In Neal Rodriguez's own words:
Back in the New York 140 Character Conference in 2010, I tried to interview television personality, Donny Deutsch, backstage, after he delivered his presentation. Unfortunately, I mispronounced his name by calling him Donny Douche. Mr. Deutsch got angry and walked.
WARNING: A decent amount of celeb-rage in this video.