Leviticus 19:19: "Ye shall keep my statutes. Thou shalt not let thy
cattle gender with a diverse kind: thou shalt not sow thy field with
mingled seed: neither shall a garment mingled of linen and woollen come
upon thee."

So if your Hawaiian shirt is made of mixed fibers, it violates the laws
of Moses. ;)
        \_ You're reading a 6th generation translation.  The passage is
           talking about not mixing races, not your tshirt fibers.