[Teegy]

This is why I was asking the panting question, Teegy has only ever stuck his tongue out when he was unhappy in an environment and I could sense him stressing, so we left.
The tongue and all signs of stress disappeared

Originally Posted by QuickSilver

I'm going to be Debbie Downer here... it's actually a sign that your dog is uncomfortable. It's an abbreviated form of the tongue flick, which dogs do as an appeasement signal when they feel social pressure. That's why it often happens when you are taking a picture of your dog, as many dogs feel uncomfortable in front of the camera.

Don't get me wrong, I think it's darling (as evidenced by my avatar), but if your dog is doing it a lot, consider backing off and giving them more space.

Some of the pictures posted here just show the dog panting, or with their mouth open in excitement. I'm talking about when just a little is showing and the mouth is closed, or when the dog is repeatedly licking their lips. Another sign of discomfort is yawning.

It does depend on the context. For instance, if you are teaching your dog a trick, he might be sort of stressed, but in a good way, and stick his tongue out. Or if he does it while he's approaching you, he's showing you respect. He's saying in doggie language, hey, I'm not here to take any of your food or toys. I just want to love on you!

When Thor approaches me, he goes through this whole series of lip smacks and yawns 'cause he's such a timid little guy.