turn all the way to the left, then back jsut a little. Sometimes you need to jiggle a little, while you turn the key to the 3rd postion (counter clockwise).
It will stop anyone from turning it other than left. Always makes me think of Derek Zoolander.
Turn it almost all the way left, and at the same time turn the key counter clock wise to the lock symbol, might need to jiggle it a bit. Dont press in to do this, just turn it real lightly. The only reason you'd ever need to press in it to open the under seat storage.