Just wanted to say that actually it was a pretty short (~2 week) phase with my dd -- dunno if that was sheer luck or how we handled it. We basically didn't make an issue of it (much easier for me since I'm deaf, probably!!
) and recognized that it was something she was going through. When she'd say "no", I'd say "OK", and go on to something else. If it was something not negotiable, like leaving the playground, we'd gradually say "goodbye" to everything, then "byebye playground!" and into the car. If she still said "no!!", I'd just mildly say "sorry, we need to go now. It's getting dark/ we have to ______/ whatever."
She pretty quickly realized that a) I recognized that she was communicating something, and respected that, but b) there were limits on what she could accomplish by saying "No!" and c) she wouldn't get whatever she said "no!" to, (offers of food, offers of activities) and she actually wanted some of those things, so saying no didn't help her.
It's not like she never says "No!" anymore (hardly!!), but it was a definite period where it was "No!" all the time, and that passed.
One last thing -- at some point we started a couple of "No!" games. One is "No/ yes!" where she says "no,", I say "yes,", then I sudddenly start saying "no", and she says "yes!" :P Just back and forth fast. Another is when she says "no!" to one question, and I suspect she's just being bloody-minded, I then ask a bunch of other silly questions. Like,
"Do you want a banana?"
"Do you want a fanana?"
"No!" (with a smile)
"Do you want a tarantula?"
By the time I get back to "banana", she'll often say "yes", IF she really wants one. If she doesn't, she doesn't.