I think Boo is a cute name. It's actually quite fitting for a goofy Dane. Just call him "Goofy Boo".
My big, fat, black housecat's name is Boo. Just seems to fit him. Although it has morphed into Booty, Boodles, Boodle Oodle, Goobs, Goobie, Goobles, Doobie, and on and on.
I wouldn't take it so personally that someone thinks your dog is a goofball or maybe a little retarded. Big dogs just ooze with personality and they are clumsy compared to smaller compact dogs, but that's just how they are. A lot of people, once they see Drake, say "It's a Goofy Newfie!" It's true, but not all the time. As much as I don't want my dog to be regarded as a ding dong, he kind of is one at times.