I'm sure any breed of dog can be nasty if it is not raised properly, however labs, by nature, are energetic, fun-loving, loyal dogs. I have three lab mixes and none of them has a mean bone in their body. They can be grabby with treats and over excited to see people some times (ie jump on people), but they are not the least bit "nasty"

To help with the grabby treat problem, I would teach "off", "wait"and "gentle". I don't know what your experience with dogs is, but if you need some hints with these commands I can try to explain...