He was spouting off stuff like "Stupid Americans!" and saying he was not afraid to get sued and that he would just return to his home country. Needless to say, I was pretty terrified. This dude was scary, and my friend (SF local) warned me about The Tenderloin.
Anyhow, I think it's great that you met such a positive and interesting character in one of the most unlikely places.
I directly saw 2 fatal shootings (two right outside the house at night, while I was sitting by the window cleaning a handgun and on IRC at 2am; called the cops who came by the next day; drug dealers -- saw a bunch of fights, dead people carried out of SROs, etc too), and got assaulted once (guy tried to grab my bag, it remained attached to me thanks to wire in the strap, some violence ensued, I ran off).
Not a place I'd suggest living if you have a choice. It may be gentrifying now, but the SROs are effectively permanent, so there's going to be a population of crazy and/or drug addicted people forever, and the criminals who cater to and prey on them.
During the day time I'd be more concerned about stepping in human excrement or rivers of piss. In fact, walking to the BART tonight from the Tenderloin I dodged 3 piles of human shit and near-missed another.
The Tenderloin and Twitterloin are blights on this fair city, and its toxic presence is oppressively pervasive if you spend any amount of time downtown (or even further out, like Hayes Valley and the Castro). It's a startling example of complete public policy failure at all levels of government.