Does this first photo scare you? Pepper not only bared her teeth but lunged and sometimes bit her people when they reached for her on the couch or approached her when she had a toy. She had her reasons. Like many small dogs she was easily startled and became defensive-aggressive when a much bigger creature loomed over her. She also suffered from joint pain.
Nobody gave up on Pepper. Her people learned to lure her for hugs and cuddling rather than inadvertently triggering her reactive fear. We also reduced her anxiety with safe medication. Antiinflammatory and pain meds helped too. No side effects. The result was a happier dog who still occasionally reacts and shows her teeth but she never tries to bite anymore. A better life for everybody.