Haha, cute grin! I have a cattle dog, so she comes with the characteristic ACD smile. They have dingo blood in them, and don't pant like a normal dog does, they don't hang their tongue out. So, when tired and happy, they get this wide, smiling pant. It forms wrinkles in the corners of their mouths, but forms more when they are relaxed. We count these wrinkles and use them as a gauge for how tired and content she is. The record was after a day at the dog park. Eight wrinkles on each side. XD. She has a special dopey grin for when she looks lovingly and deeply into our eyes, and a ridiculous goofy front teeth grin where she rolls around like a nut to elicit play. She doesn't do the real doggy grin that a lot of the loose lipped breeds do, where they hang their tongue out, smile wide and doofily, and roll their eyes to the side at you. That's one of my favorites!
Ha, your dogs sounds like a character..and, I know exactly what you're talking about when it comes to the hang out the tongue smile..I see that a lot in the mastiff type dogs..big ones like that. :d
I fostered a beagle once, they are great dogs too. Nose to the ground kind of guys! She was stink..wanted to get up on the counters. Since I was fostering, had to break her of the habit. Poor baby, she loved the counters.