First, I came to a 4-way stop here where a Waymo car had arrived and stopped maybe 1-2 seconds prior. Waymo was on 15th heading East, I was on San Bruno heading north. Nobody else was at the intersection: https://goo.gl/maps/S2GmNTuWNDq
I stopped fully and gave it about 2 seconds to start moving since it had right-of-way. It made a one or two false starts, then I just gave up and went through the intersection because it was clearly having issues. Looking back in the rear view I saw it did the same thing with the next car. Maybe it didn't think it was a 4-way stop or something?
A few minutes later, I was on Bryant just past 7th outside the Hall of Justice in dense traffic that was moving quickly (as people do on that street). A Cruise Automation car (I think?) was in one of the right lanes next to me and, for whatever reason, decided it wanted to get over to the left quickly. When it didn't get a good opening after a couple seconds, it more or less stopped in the middle of the road to wait for an opening. Unsafe and almost caused an accident with the cars behind it.
Of course human drivers do stuff like this or worse all the time ¯\_(ツ)_/¯ It's going to be interesting to adjust to all the ways these things behave unpredictably (relative to what we'd expect from human drivers).