This one is a classic, and doesn't need a lot of explanation.  A fast-food chicken chain in the US - Chick-Fil-A - just had their annual "Cow Appreciation Day" where they invite people to dress like a cow and get a free chicken sandwich.  The consumer participation is strong, media think its hysterical and the company has found an annual celebration that provides a nice personality for the brand and a great way to drive awareness of the company in the heated fast-food market.

I like it - not sure I'd dress up like a cow for it, but, well, of course I would.  Go Chicken!