Not too long before I found the Dash site I was helping some friends fix up a house they had just purchased. It had a lot of woodwork that was painted over that they wanted stripped off. There was one door that was being very stubborn. I tried everything- a heat gun, chemicals, etc. The paint was just not coming off. I wailed away at it for hours and hours. My friends told me to stop or take a break. I refused, lol. They said you are such a bulldog and started calling me that. When I found the Dash site I thought bulldog sounded like a good butch screen name. So I chose that and have been BullDog ever since. I do think it suits me. I may be just a little stubborn.
As to Bully, Hank and some others were the first to start calling me that on the Dash site. Quite a few people call me that, here online as well as in real life. My former roommates (butch femme couple) call me Bully and they haven't been on a bf site in years. Their whole family does as well and other people they have introduced me to.