My avatar is the only photo I've got of a "mean face".
Funny thing is, he was YAWNING when I snapped the photo. I thought I'd gotten him with his mouth wide open, but when the pics got developed I was suprised at what I saw. He always retracts his lips and wrinkles his nose a little right before he shuts his mouth after a yawn. I'm just amazed that I managed to get a pic of it, entirely by accident. :)
This dog, and my 50 lb mutt Chloe are the only 2 of mine who do a pretty good "mean face". Chloe is one of the most people-loving dogs I've ever met. But when I roughhouse with her you'd think she was planning to tear me limb from limb. She'll bare all her teeth and growl/vocalize with her mouth open, looking savage as all hell, but she's never so much as laid a tooth on my skin even by accident. And when she barks at an approaching stranger or someone at the door, she's got that bark where she looks right at the person and you can see a healthy white flash of teeth every time she opens her mouth. I like that fact, nice to have an alarm barker....lol....even though I don't think I could count on her to do more than wag-and-jump a burglar to death if one actually came in the house.
One of these days I'll try to get a good shot of Chloe's mean face. Hers is much more nasty looking than the dog in my avatar. Especially now that he's 9 yrs old and he's had his top 2 canines removed (tooth injury)....so now he looks a little funny if he bares his teeth. Poor guy has always had problems with weak teeth, tends to be hereditary in the breed....if he keeps it up we'll be feeding him mashed bananas with a plastic-coated safety spoon before too long. :)