My 7 month old puppy is generally good with strangers and frends. but my best friend comes around and he acts like someone is trying to kill him. Angry or scared barking and tries to knock the door down and no control. This only happens with this one guy. has been going on for about 4 months now. ive had him ignore him and throw treats. hes been a best friend to all of my dogs for the last 30 years and i cant figure it out. its really bothering me. If anyone can help I would truly appreciate it.