Let's start with a "for instance"...You're walking down the street and a stranger hugs you then says hello. How would you react? I'm guessing there's a range of answer from being stunned and freezing to punching the stranger in the throat. Unless the drinks are flowing we don't usually have the "I love you man" reflex as our go to, we tend to like our personal space. Some enjoy more than others. Here's a simple diagram showing different levels of personal space.
Each person will have different space requirements within each level but the levels remain the same for everyone. Dogs have similar requirement to us when it comes to personal space and that space needs to be respected. Not every dog loves receiving cuddles from strangers, it can equivalent to the scenario noted above. And like that scenario each dog will have a different reaction to having his/her space being invaded; some will try to retreat, others may feel threatened and bite the stranger.
If you're walking down the street and cross a dog on leash that you want to pet, ask the owner first and only when you hear them say yes should you interact with the dog. Make sure you WAIT for the answer, too many people will ask if they can pet a dog while they are already reaching down to pet the dog. Don't be one of those people. The handler knows the dog best and should they say that you cannot pet the dog you will need to respect the decision, it is for your and the dog's safety.
And while we're talking about polite hellos let's stop the eternally believed "put your hand to the dog's nose so they can smell that you're friendly". This is not ok, nor is it safe. There is no way for you to know the dog's history by just looking at them, some dogs may have a bite history, some are anxious or fearful and others may be in training. The main danger is if the dog has a bite history...you may get bit and severely hurt. Just that should be enough to spot this long standing process. Should the dog be anxious or fearful and you invade their personal space it can be perceived as a threat and again you may get bit. If the dog is in training than you may be inadvertently teach that dog something the handler does not want. For example: Service dogs need to be trained to ignore people around them to focus on their person. By throwing your hand in the dog's face you may be undoing someone's hard work.
I'm sure you can tell by now that people petting unknown dogs without permission is one of my biggest pet peeves from the dog world. The main reason for that is if the dog snaps and defends his/her personal space (which is perfectly normal if the stranger invaded their space, remember the for instance at the start) then he/she will be labeled "dangerous" or "reactive". Now the handler is left apologizing for something that, in my opinion, they should not have to. The dog is officially labeled as "bad" and now the owner has a tons of work to do with that animal to bring them back from that experience. All around not fair!
So how can I pet a cute dog?
The proper way to say hello to a new dog is to interact with the handler first, speak to them (trust me just this will make their day, we're used to being on the ignored end of the leash!), ask them if it's ok to pet their dog. If they say yes, don't just jump in the dog's face! Hold your hand out a bit, just a few inches from your body and let the dog choose to come sniff you. By letting the dog initiate the interaction it makes sure that the dog is comfortable, this lessens the chances of the dog being scared, and/or potentially biting you.
Here's the part that a lot of people struggle with...if the dog decides not to interact with you you have to walk away! Don't believe yourself a Disney princess that every animal has to love. Some dogs enjoy having people near them but not touching them, and that's ok. Others may be having an off day where they don't want to cuddle, maybe they're grumpy because their diner's late or they didn't sleep well. It happens to all of us, 2 or 4 legged.
As the handler it's your job to read your dog's body language and make sure he/she is comfortable with the interact. If your dog looks uncomfortable, anxious or scared it's up to you to end the interaction and make sure your dog gets the space he/she needs. The more positive interactions your dog has with strangers the more comfortable he/she will be interacting with them (whether it's being around them or receiving cuddles, again every dog is different).
So here's the moral of the blog post....Don't pet a dog you don't know before asking for permission and don't stick your hand if their face!