The creepiest of those things I've ever walked by in a store was a big plastic sunflower that suddenly opens its mechanical eyes and exclaims "Hello!", followed by a rendition of "You're My Sunshine". I should have bought it just to see how far I could kick it, and how many pieces it would be in when it lands.
Another time, I was in a grocery store around Halloween time, near a whole display of these little witches that cackled, played creepy music, and said all the usual Halloween phrases. The guy sweeping the floor nearby (presumably having had to listen to a few dozen of those things all at once for days on end) suddenly yelled "Shut up!" at them.