I think I know this look although I can't really fake it that well myself and I'm not gonna post myself in the public section
anyway the look is confident, playfull, trustworthy and calm. that's how I would best describe it. When doing it I think I always have a sort of half smile on my face and am very laid back, mostly I have my arm around the girl, and havn't really done anything to break her trust. (no weird routines involving some kind of strange premature handholding.) To get this look it is important to NOT lie AT ALL. Don't say your a dancer if your not, they will catch on and you lose the trust required for this look.
PS. I havnt read a lot by swingcat, (not enough hours in a day to read!) so, I hope this is what you were looking for, I'll check if I can make a picture of the look (The lighting in my room is 200% against me making pictures!) and post it in my picture thread.