You don't even know the meaning of the word 'Ju'. lol.
That's funny. Someone who practices self defense and doesn't know about that word. Besides, Brazillian Jiu Jitsu is mostly ground work. It's not because we practice ju jitsu that we keep it just limited to techniques. We also try to learn new ways to defend ourselves from realistic attacks.
Hence why I started this thread. That attack is one of them. It is realistic that someone would come up to you, grab your collar, put a knife to your body and ask: "Give me your money".