It's one thing to throw a punch faster than the teacher wanted for demonstration purposes, or to misunderstand and throw the wrong punch or a kick...I've seen it happen by accident to Hatsumi-sensei. He still flattened the idiot, then made him get up and do it correctly this time.
"Accidents" such as punching with the wrong hand as the kata, kicking by mistake, coming in *WAY* too fast, are good for you--not in the sense of learning the kata, but in the sense of knowing whether your body automatically handles itself. If you have trained properly, things will come together naturally....
This is very different than "sparring" which creates anticipation and instills a sense of being "on guard." My rule is that when these accidents happen, let the body handle it naturally, even if it means that you do not actually do the official technique. So long as you are safe, everything is good. One cannot be captured by the technique.
Then go back to doing what you are supposed to do, and listening to the points that the teacher is emphasizing. A good teacher that is paying attention *MAY* actually build on what just happened to you, and address it. Hatsumi-sensei does this all the time!
In the end, you should go back to thinking about how the technique could be adjusted to reflect that "accidental" dynamic by yourself.
Just some thoughts.
-ben
And I ALWAYS want students to punch AT ME when I'm trying to demonstrate, not at some guy 2 feet to my left or right that nobody else can see...
I typically want the punch thrown with speed and intent, as well; I'll tell them what speed I want if I want it thrown slower, for example...
The first is an accident; they happen. I'll roll with it. (OK... I damn near cleaned one guy's clock after the third "accident" in a row when I was trying to show something...) The others are required for me to demonstrate what I intend to show.
But if someone is deliberately throwing the wrong technique or otherwise screwing around as they're being honored to be used to demonstrate a technique... That's beyond rude. I always learn more in the "demonstratee" or uke role; I have an incredible view of the technique and how it's supposed to feel there. I'd have very little patience with a student who decided to test me by purposely throwing a kick instead of punch, or something like that. And , I suspect, that my lack of patience would probable end up with someone falling down... That sort of stupidity is robbing all the students of the opportunity to learn!