I think that the borderline between sprezzatura and ritardato can be quite subtle. As someone mentioned in another thread, item 9 listed by Soph ("Thin part of tie below top") may be more on the ritardato side.
I sometimes like to leave the thin part loose (that is, not held within the loop of the back side of the wide part); I hope this to lend a touch of sprezzatura to my look, allthough I fear that some people think that it is rather ritardato. Other people probably think that I do it just to show that my ties are Ferragamo ties. (I guess this is why some brands, like Ferragamo, Hermes and Loewe, also put the logo on the front of the thin part of the tie, instead of only on the back of the wide part).