Is the dog mad or playing?

One of my shelties always breaks into a fit of barking if I stick my tongue out and blow, or if he hears me just blowing air. He comes running and starts barking at me, and sometimes will stand up on his hind legs and push me with his front paws. I play this game often with him, but I can't tell if he's actually mad or if it's a game to him too. Don't wanna keep it up if it really is offensive to him for some reason. Any thoughts?

When he rushes at you, barking, are his ears up, pointed forward, or laid back? Is his tail wagging or down? Those are the clues to see if he's excited or anxious. Shelties tend to bark in either case, so the rest of his body language will be a better indicator!

I knew a beautiful Standard Poodle who was terrified of anyone blowing in her face, after a not-dog-knowledgeable co-worker used an air hose pointed at the pup's nose when she was just 9 weeks old.

Well, his ears go down for just a moment and then come back up, but his tail is always up above his rear. Sound like playing?

That does sound like playing, like he's enjoying it, but I would watch his body language carefully, just in case!

I used to ask Tyler the Sheltie "where did your ears go?" when he was very, very happy, they'd be so far back they'd be invisible!