Re: What technique would you apply to neutralize Brazilian Jujitsu attacker
The "boasting", as OP put it, of some BJJ practitioners happens because BJJ has a long and well-documented history of making fools out of martial artists who don't know how to fight on the ground. If you want to defend yourself against a BJJer, you need to practice two things:
1) Keeping your feet against someone who knows how to properly use BJJ-style takedowns, and
2) Defending yourself on the ground against BJJ-style grappling.
Needless to say, these are not things you'll get to practice much in most aikido dojos.