That video clip is like my worst nightmare (ok, maybe the girlfriend with a knife or gun would be worse, but not much
). All you can really do is train hard at the best dojo you can find, try to stay aware, and hope for the best. The fact of the matter is that probably 95% of all people would fail in that situation, regardless of art (outside of gun-fu). Kudos ot the 5% that could actually pull off a defense in that situation.