I guess we got lucky, considering how many years we went door-to-door in the South Bronx and the projects in the 70s, 80s and 90s. No guns, no threats of violence. Well, one pair of boys confronted me one time, but they didn't really seem like the type. One of them mugged and postured, and I just kept staring at him, unimpressed. His partner slapped the back of my head and both ran away, giggling. They were young and not intimidating, so I just sighed and went on my way.
Another time, we knocked at a door and waited a minute or so, then left. As we were walking away, the homeowner came out, waving some magazines and complaining that we wouldn't leave him alone. Apparently, some pioneers had worked that block during the previous week, and I guess the extra visit was one knock too many. He didn't do anything aside from yell at us, so we left and decided to work another area that was hopefully not as recently worked by careless pioneers.
Other than that, we had the occasional door slammed in our faces. But I was never in a situation where I felt frightened or intimidated.