Hi, i was walking my dog today and he met another Cocker Spaniel, instead of sniffing him and saying the usual hello, he growled at barked at him, nothing serious, he ignored him after i pulled him away.

But then he met a dog that was twice the size and was all friendly and playful with him

Iam guessing they are like us in a way, for example we may like our friends but some people we would not want to get along with i suppose?

I think this is interesting about dog behaviour, lets discuss it!

My Hyzzie is insane she was feral when I got her and took some taming. She's half mini pin but is terrified of any mini pin she's ever met *shruggs* maybe bad memories of her first home.

My other one loves all little ones but hates big ones but they've had some bad experieinces with big ones. Quasi wants to fight all big dogs. He especialy loves little white fluffy dogs.

Hyzzie tends to like black dogs big or small.

Well, I have a 6 pound Chihuahua who will growl at my 160 pound newfie while biting his nose, then after about five minutes, she'll roll on her belly and submit. And after that she'll go and cuddle with one of the two smaller dogs....

Well dogs i really cant evan begin to explane for one thing i have no idea why they att eachother

Agression, fear, panic, loyalty; many things can make a dog want to fight with anything. Dogs who've been "bullied" around by other dogs will develop a fear and agreesive nature towards other dogs... That's just one expample based off of White Fang.

Maybe defending their territory, mate, offspring or owner. Who knows? There are lots of reasons.

My dog hates border collies. I think it's a personality clash

Some dogs are just more dominant than others either because of their nature or because they've not been trained correctly, and are more likely to be unsocialised. Other times, they react to the "language" spoken by the dog they meet (staring in the eyes is not a good sign!) just like we might, if someone was rude to us.

I'd pretty much equate it with why people fight.

I dont know how, but this question triggered a lost memory of when I was a kid.... I saw two dogs fight real bad that one time...It was at a campground (and this is also way before we got our dog Lucky, for the record), and these two dogs, just down the road from our campsite were fighting (I dont remember how it started, at this moment, just that one thing I was walking down the road, and the next thing, boom, they were fighting not two yards in front of me, and everyone from the nearby campsites came to see what was going on..)...they had been fine with each other up until that point, and it was a surprise to everyone...

I remember both dogs were injured, as well as one of the owners when she tried to stop the fight...it was a real vicious fight..And the real strange thing, if your trying to equate this to a human fight, is that these two dogs (collies, I think they were, if I remember correctly) were father and son! really! So I have no idea why they all of a sudden began fighting right in the middle of the road

on a side note, my parents apparently thought it was a tramautic experience for us kids who saw it, because I remember for the next few hours at least, they were trying to comfort us and such and tell us it was all right...I admit I was a little shaken at first, but I was more mystifyed as to how this fight could have started, and a little sad about the two dogs..I have no memory of what happend to those dogs after that, unfortunately

Well, about the two Collies fighting, who were father and son, supposedly; the only thing I could think of could be a dominance issue or something. Since I think wolves attack the "Alpha" whenever they want to take its position.. so maybe the son was attacking its dad because of that.

Just my theory though, lol

Into dogs biting children, it may hold some merit into dogs fighting (other than those trained and abused to do so for entertainment) each other for reasons not immediately apparent to us.
Let me start by mentioning an observation of my own, and of many other dog owners I have spoke with on this subject at dogparks (of course many times backed up by the owners behaviors).
A large number of adult dogs that attack other dogs (seriously, not play fighting which some owners dont know what the difference is) has to do with how they were raised and are kept at home (sometimes those that are spoiled way too much are more apt to start a serious fight for dominance), but this is only in some cases as the dog park is a neutral territory.
A big reason also has to do with dogs that are not permitted by their owners to playfight and socialize as normal dogs and puppies do with others when growing up. They do not no how to communicate with others and settle simple disagreements and social encounters as they should, instead they take all disagreements, stresses, and challenges as a serious situation that needs someone to be injured or killed to settle them, after all their owners taught them this by depriving them of a normal social behavior.
Another problem has to do with encounters between fixed, and unfixed male dogs who are either on a leash, inside fencing, or in a building, sometimes by the presence of a female dog, especially in heat. Unfixed male dogs are many times more likely to start a fight either through sometimes unnoticed body language challenges, and/or direct challenge/bluffs.
Dogs restrained by a leash, a chain, a cable, a fence, are all going to react to an intruder, a nearby canine, or human in a way that can cause problems or fear, but this is because they have no place to go, and because both dogs build up frustration by being near each other but unable to get close to socialize properly.
Another factor that directly affects them, their owners attitude, the owners stresses, and the dogs ability to read these, which they sometimes react upon other dogs in responce to this. It is common to hear owners of dogs mention that certain owners of certain dogs are real jerks, their dogs mirror the owners thoughts and behaviors, after all they are learning by example.
In the article dogs attacking kids under 6 were overwelmingly from unpredictable, fast,sudden,and loud behaviors from the kids, which scares or spooks the dogs.
Those who bit kids over 6 were overwelmingly a responce to what the dog percieved as a threat to its food, territory, toys, or dominance.
The suprising result was medical problems, most of the dogs examined by authorities after attacks on kids by professional vets showed physical maladies ranging from liver/kidney problems, digestive problems, skin and hair/fur problems, etc that caused them to have a much shorter temper. These problems were mostly unnoticed or unknown to their owners, Im sure some knew and did not care at all..
Keep in mind that most of the dogs and kids involved were familiar with each other, were around each other regularly, and had no signs of a problem apparent to the parents or owners.
There are many factors involved.
Complex subject.

I think they can sense something with other dogs, they may view some (or smell them out) as a threat and have to defend themselves. I think it's all has to do with senses. It also could be that dog is unsocialized with other dogs and may have done some movement that your dog interpreted as a fight maneuver or a "back away from me attitude".

What everyone else has said here is true too. But I see that this post was made in November! So how is your dog now?