I've heard this called the "California No," in both a personal and professional setting. Apparently it's extremely common in Hollywood and that's where the term came from. I've definitely noticed as I socialize in California that people avoid perceived confrontation more here, so maybe there's something to it. A new one I've noticed recently is what I call the "read receipt no," where someone will read a message, send a read receipt, then not reply to say no.

If someone does it to me I tend to lose some respect, but that's possibly because I'm an outsider. Maybe Californians expect that but I usually hope for the respect of a direct no. (Shrug.)