@agilebasenji:
Instead of saying "My dog isn't friendly" or something of that ilk, which can perpetuate that myth that basenjis are vicious, biting dogs (and I have encountered those people in non-dog areas of life), you may want to say something like "My dog is recovering from mange" or another contageous disease. (or just "my dog is ill") That usually gets people's attention real quick.
I think it is important that people learn to think twice before they let their dogs get in another dog's face because 'their dog is friendly'. I don't really care what they think of the breed, or my own dogs. If I know the person, or have reason to talk with them beyond trying to keep them from letting their dogs irritate mine, I will explain that my dogs aren't nasty, they just have very clear rules about how dogs should approach each other.
It isn't a myth that basenjis on lead are often likely to growl or snap at dogs that approach in a reckless fashion. And, as Lisa said, usually dogs that approach like that aren't 'really' friendly, they are rude.
Personally, I would rather have someone think my dog is an introvert than sick