My first two weeks in SF I took the bus twice, the first time a group of kids started slapping random people, I was prepared to fight and protect my SO but they didn't get to me; the second time some guy just ran and took a girl's phone, she grabbed to it for what seemed like a full minute, screaming and shit, then finally let go... I was paralyzed, especially after the event of the previous week, after that I vouched not to ever take the bus again in SF.

After that some homeless people screamed at me, some tried to punch me slowly (easy to avoid), I got used to it with time but it's still not a nice feeling to take walks. I wouldn't let my SO walk alone at 3AM through the streets for example (while I would have no problems with that in London or Beijing).