If I ever got into a martial arts fight with some dude, and he said he was about to use tae kwon do on me, I'd say "oh yeah? Well tae kwon DON'T" because I think if anyone had a great comeback like that it'd be hard to beat them to death with their own foot.
Martial arts seems like one of those things that is a great idea until you realize you can basically never use it. Just imagine--here you are in a board meeting, and that squirrelly guy from the Customer Research Department makes a crack about your tie, it's not like you can just leap over the table and give them a roundhouse kick. He'd likely lift up his three ring binder and block you with it, and you'd fall back into the end table with the water pitcher, making an awful mess.
Or you get cut in front of at McDonalds. This actually happened to some guy last time I was at McDs, in the line next to mine. He got all irate but the guy who cut in front pretended not to speak English (which, by the way, is a clever tactic, but doesn't work at aforementioned board meetings, where they already know you definitely speak English because they spoke to you before). The irate guy tried to prove the line cutter could understand English, by saying really insulting things, but got no response. The line cutter was ice cold.
Would kung fu have worked in that case? Probably not--it was crowded enough that Irate Man would likely have connected with my face while trying to roundhouse Line Cutter. And while I was simply trying to get a milkshake like any proper gentleman, I would have certainly joined the fracas, turning a basic Chuck Norrissing into a full-blown Road Housing. And, for all we knew, Line Cutter was armed.
Movies make it look really easy to disarm someone, because they always hold their gun or knife limp wristedly, and way in front so all you need to do is quickly kick the wrist and the weapon drops harmlessly. But if the armed goon is more than a few feet away from you, you'd have to move in close to get at the weapon, by which time they can usually pull the trigger or do some slashy motion. So maybe kung fu was great in the days when people were armed with only their wits and maybe some sticks, but these days it's really just for show.