A lot of my verbal confidence comes from physical confidence. I'll add that I'm not that swole but Krav self defence has really helped. Body language confidence is definitely a thing that people pick up on. Less so for socially inept and unaware fatties... they think their size is intimidating and they increase their volume to try and get their point across. I just employ eye rolls and frown whilst saying 'really' at those that try to talk over me. That also seems to work well. Sarcasm is your friend!