I've found the word "reactive" is often used to candy-coat what is actually "aggressive" behavior in dogs.
It seems to be a blanket diagnosis some trainers and behaviorists pull out of their hat any time a dog is confused, insecure, or just plain spoiled.
A truly "reactive dog", meaning a dog who is chosing flight over fight, is one thing. A dog who claims space, disciplines humans, and moves into another being's space in order to "get them before they get me" is behaving in an aggressive manner.
IMO