Re: Don’t waste your time practicing AIKIDO
You've made your choice to do aikido. So why waste your time proving or disproving aikido's effectiveness? Simply agree with them and admit that aikido is absolutely useless in a street fight. Ask for a demonstration of their prowess (not on you of course), and look for every opening in their attack and defence. Then thank them for their impressive display of martial effectiveness and say you are too much of a sissy to take such hard punishment and that you'll stick with a sissy sport like aikido instead. And walk away.
The most frustrating thing for people like this is if you don't play their game.