At training last night we were waiting for the class to start and sat next to a 9 month old lab.
He is friendly but when he was saying 'hello' to George he started snapping his teeth together.  I've not seen a dog do this before and the owners weren't concerned as it is something he does a lot I think (I've only been going to the class for 2 weeks).

What could the snapping teeth mean?  He wasn't lunging in an agressive way but more like just banging his teeth together.

were they snapping really fast, with his lips in normal position, alsmost like he was shivering witth cold? my pup has just grown out of that (hes 7 & half months), he would do it when he was really exited about meeting somebody new The only time I've seen this before, was with an entire male of mine years ago, if he found a really interesting smell on the floor (bitch in season) he would do it.

No not really.  It wasn't like chattering teeth at all.
He would just walk up to him and almost like snap his mouth shut and then again a few seconds later.  His mouth was opening when he did it but not as if he was going to bite or mouth my dog.
I guess it could have been excitement due to the environment.

My first Dobe used to do it. It was just a means of communication with her, as if she was trying to say something.

It probably was just exitement or communication, as Pedlee said.

It just goes to show that weather a purebreed or not, they each have thier funny little quirks
My pup has another funny habbit, if he is sat down and we are talking about him/looking at him, sometimes his rear foot will come up as if he's going to scratch his ear, but it doesn't actually touch his face/head atall, his foot justs stays ther in mid air!!! We call it the 'phantom foot'. I'm not exactly sure what it's all about, I think it may be a calming signal when he feels abit uncomfortable with too much attention??

My cat does it when shes sat at the window and sees birds in the garden but cant get to them lol

Yes!!!  It was just like that thinking about it.  I have seen my friends cat do this but she is evil anyway

I'll keep a look out and see if he does it again next week!

My newest dog did it a lot when we first got him but not even at our other dog, just as he was wandering around sitting having a fuss. He would just open his mouth and close it so his teeth make that 'snap' noise and like I said it was never directed at anyone or anything and he would often only do it once or twice then stop for a while. When we went to pick him up he was doing it a lot in his old home but as he's settled in he's doing it less and less. I though perharps it was an excited thing or a nervous thing (we went to visit him in his home then he had a long car journey back to his new home). As I said hes doing it less and less and it doesn't hurt anyone so I leave him to it, I think within the next month or two he will have stopped completely.

My boy does it sometimes (he is 3years old) especially when I am heading toward the cupboard to get his food.  He just stands and raps his teeth together maybe a couple of times. Thats it nothing to it, it is just something he does - maybe he is saying "get a move on with my tea".