She Goes Crazy around hats?

Bella has never been mean or agressive toward a dog/cat/baby/adult human etc.
She licks kittens and my friends 18 month old daughters, and she plays with the adult cats.
But when shes out front on her chain to eat and potty.. she goes nuts, - but i dont think that if she ever got loose she'd attack anyone.. she got off her collar once when no one was on the road, just ran around like a retard then ran back to the door ready to come in. :P
Anyway, our friend Michael works at mcdonalds, and he came by one night after work, and he was wearing his mcdonalds hat, as soon as he walked in she acted like she was going to bite him and growled at him. I immediately screamed "TAKE OFF YOUR HAT, TAKE OFF YOUR HAT!"
and once he took off his hat she was fine.
Do you know what causes this or if there is a way to break her of this, she also does this with larger people [my friends girlfriend is pregnant] and shes fine until harley turns around then she goes after her.. thankfully she was leaving and closed the door in bellas face.

I'm not sure whether it's normal to chain up dogs in your country, but in this country, & especially amongst the dog-loving community, we would never dream of chaining a dog up & leaving it, & absolutely never, ever attach a chain to a dog's collar . I don't mean to be harsh & I apologise if I've got the wrong end of the stick, but I don't think leaving a dog tied up to anything is a very wise thing to do.

In the first place, the dog could end up choked or strangled, secondly, it is at the mercy of any other dog, person or other animal that could do it harm & thirdly, by chaining a dog up you are asking for the sort of behavioural problems you describe. I don't know if it's feasible in your case, but what if a small child was able to approach the dog? It could all end in tears.

Dogs have flight or fight reactions the same as any other animal & by chaining the dog up you are taking away its primary self-defence mechanism of flight. The dog then has no option but to use the fight mechanism if anything scares it. It knows it can't get away so the only thing it can do is act aggressively to try to get rid of the scary thing!

So whether it is a person in a hat, or a pregnant lady that makes the dog feel anxious, the only thing it can do is to bark, lunge & try to drive the scary person away. Yes it may calm down when it realises that it knows the "scary person", but it will still have all that adrenalin flooding its body for some time afterwards & because of this it will still be much more inclined to be more reactive for sometime afterwards.

Plus the more the dog "practices" these sort of "fight" behaviours the more readily it will react in this way again ~ so the problem escalates & the dog starts to react to other things, like traffic, other animals, noises, then to all these things even further away. It can be a vicious circle of deteriorating behaviour if you aren't careful.

Your best bet is to stop tying your dog up. Then calmly & positively introduce the things that you think scare it, firstly from a distance & use lots of praise & treats for not reacting & being calm. Then introduce these things at gradually reducing distances as long as your dog can remain calm (sitting or lying dpwn perhaps with its attention focused on you?).

I do hope that I've got the wrong end of the stick though, & that you don't really chain your dog up by its collar & leave it unsupervised.