My in-law’s dog Heavy does this thing with his lip when he’s stressed out or doesn’t get his way, like when we wouldn’t let him inside while we were eating dinner the other day: 

His previous family called it the Elvis snarl, haha. I think it’s a hilarious look, but it’s also cool that he has such a clear way of communicating to us when he’s stressed or unhappy. My dog Lulu’s stressed-out signals are more subtle so she’s harder to read, but we’re getting to know her better (side note: she seems happier in her new routine and is doing well with training since we got her back from the trainer, yay!). So while Heavy’s right-in-your-face style of communication can be annoying (this snarl is only one of the many loud and/or disruptive ways he communicates), at least there’s no uncertainty about what he wants or how he’s feeling.