Artist Mark Wagner takes one dollar bills and cuts them with an Exacto knife, then reassembles them into works of art that sometimes have no resemblance at all to the original bill.
The one dollar bill is the most ubiquitous piece of paper in America. Collage asks the question: what might be done to make it something else? It is a ripe material: intaglio printed on sturdy linen stock, covered in decorative filigree, and steeped in symbolism and concept. Blade and glue transform it-reproducing the effects of tapestries, paints, engravings, mosaics, and computers-striving for something bizarre, beautiful, or unbelievable... the foreign in the familiar.
Link -via Reddit
The key words to understanding section 333 are "with intent to render such bank bill, draft, note, or other evidence of debt unfit to be reissued"
Most people will understand this as defacement (such as shredding) so as the bill is no longer able to be used as a bill (i.e. no one would take it). In reality, in means more along the line of defacement so as when the bank takes it as a deposit and realizes something is wrong (likes it's half a $20 and half a $2 taped together but counted as $20). Now the bank can't re-issue it.
Bottom line, it's not illegal to tear up your own money.