I grew up with both dogs and cats, and enjoy the company of both. I've also studied the body language of wolves so I could write more believable canine characters, and then did the same for felines for the same reason. That's my advice to you: Investigate and learn, rather than fear in ignorance.

You have been given some -bad- advice by Explodingbat:
-If you meet an aggressive dog (not a scared one- make sure you can tell the difference!), acting like you're the top dog may get you bit.

-ANY dog can be psychotic if it isn't trained properly, or if it was bred by a careless breeder focusing on appearance rather than temperament. ANY DOG. On the flip side of the coin, a well-trained, well-mannered dog can easily come in -any- size.

Hallan