It's funny, I don't see it on the list but by far the biggest taboo in SV in my experience is talking about things going badly. You're doing great, killing it even, or you should keep it to yourself.
now that's taboo.. so taboo it doesn't even make the list because people can't even think it :)
I don't know if it's really specific to startup. In life in general no one cares about you and people tend to avoid you if it's going badly (except very close friends).
Well, I grew up in NYC where sarcasm and cynicism reign supreme. SV culture is really jarring.