I was like 7 or 8, I think, and it was a crappy SAK clone my parents gave me... When I was 9 or so I realized what a piece o' poo it was, and took it apart to see how everything worked; then I used the blade to make a fixed-blade knife with a paper clip and a popsicle stick (I probably would have been better off just sharpening the stick). I think I still have that thing, actually.