surreal-
So they say "Just trying to be nice...." Pat 'em on the arm. Entertain it. "We seem to get crossed like this often enough, don't we?". Honestly, surreal, you do not have to 'take a stand' for people to know you won't engage in their bullshit. By not participating in their crazy-making dialogues, you are speaking loud and clear. Without saying, you are saying: "I don't have time for this business, this is not my style." People cannot engage you in it if you're not a willing participant.
Say one day you choose to say, should a similar situation arise again "Hey, woman. You were supposed to help me with his furniture. Are you coming?" And she says blah blah blooh blooh, hippity hoopla, yadda yadda. Ever use the broken record technique? Educators often use it with young students...I find it still effective in particular situations. I have to use it at times with clients at my job, when they're flying off the handle.
Oh, another thing, Surreal. Have you ever heard of Toastmasters?
http://www.toastmasters.org/