8 month old border collie bites dogs he doesnt know. Help.?

I have two lhasa apsos (5 years and 4 years old) and one border collie who i got at 8 weeks old. When he first met other dogs he was fearful. I have alot of friends with dogs and attended ringcraft training for the show ring. He plays with a variety of dogs. He started nipping puppies he didnt know at 5 months old, this has now progressed to adult dogs he doesnt know. He bares his teeth (no growl) and bites them til they run away. He has also a bigger problem with boxers, one retaliated and he fought back and when we met her again she avoided him and he still wanted to fight with her. Can someone help please.