You were away…..I had a bullboxer (mastiff/boxer mix) years ago that was like that. Looked like he should be mean as hell... But the dummy was scared of his own shadow.
I moved to a different state several months ago and Dude and I were in a hotel for an extended period. We were in the room for a few days, and one morning while brushing my teeth I noticed Dude sitting in front of a full length mirror (he had never seen a mirror that close before)….. he was practicing his “mean dog” face…..curling his lips, showing his teeth in different ways. It was hilarious.