A Klein Bottle is a geometrical wonder. It's beautifully shaped, but has no distinct "inside" or "outside". It would be the perfect gift for anyone with a love of geometry - or pretty glassware. the primary purveyor of such objects is Acme Klein Bottle, owned and operated by Clifford Stoll. As he describes it:
At last, Acme has conquered topological and engineering frontiers to manufacture genuine glass Klein Bottles. These are the finest closed, non-orientable, boundary-free manifolds sold anywhere in our three spatial dimensions.I think they would make the perfect geeky wedding or housewarming gift.
These elegant bottles make splendid gifts, outstanding classroom displays, and inferior mouse-traps. With its circle of singularities, an Acme Klein Bottle can be said to exist inside of itself -- especially handy during time-reversals.