Well, less of a "redneck" vibe, and more of a subtle "I can't imagine living in some place so much less dense, and I can't see why you would live there other than it being cheaper." I think sometimes this is misinterpreted to be harsher than intended.

Sort of a "it's a nice place to visit, but I wouldn't want to live there" vibe. Which, to be fair, is exactly how I feel about SF and the metro area around it.

Ah sure. IME, that's a pretty neutral & symmetric observation: I can't imagine living in Marin (at this pt in my life) instead of DT SF because it doesn't suit me in the same way. This is compatible with your observation that you feel the same way about SF.

What's the opinion of Oakland? Or, say, Modesto?

I think Oakland is seen as pretty cool and edgy. Modesto...oh well... I'm pretty sure it's very much looked down on.