Here's What Happens When You Try to Stab an Apple Watch
To see, Unbox Therapy decided they were going to perform a scratch test on the Apple Watch Sport's Ion-X display using a key, a knife, steel wool, regular sandpaper, and rougher aluminium oxide-based sandpaper. Now before Apple fanboys squeal in anguish, the video only uses Apple Watch displays -- not the whole device.
It turns out that the key, knife, and steel wool didn't cause any visible damage to the display, meaning your Apple Watch should be ok surviving on a day-to-day basis. As you might expect, the sandpaper did manage to cause some serious damage. So don't go storing your watch in the drawer with your prized sandpaper collection, that's apparently not a very good idea.