Quick Rant: dealing with people who say 'This is easy'

Ok, so in my experience I have seen many people put varying amounts of effort in to doing exercises. "You only get out what you put in" being a popular old saying that springs to my mind.

So, take any exercise such as leg raises (Abductor lifts) while lying in the ground - these can be quite hard going if you have the position correct. It can also be extremly easy to do if your body position is wrong.

In my current TKD class I have someone who all too often says "oh, this exercise doesn't touch me" and it is plain to see that they are doing it wrong. They are a senior grade and, in my opinion, should have the attitude where they are always looking to improve themselves in the training. They should be looking to do the exercises as well as they can and try to get maximum benefit and NOT doing the exercises wrong to make themselves appear 'really fit' and worthy of their station / rank. In actual fact in just makes them look bad as if "Look, they can't even do the exercise correct", doesn't set a very good example does it?

Anyway, what I am getting to (and not very quickly) is this; when this person is behaving as described and when they don't take criticism well how do you approach it? Last night I said to this person that they could in fact do the exercise properly and then they might get some benefit from it, I got snorted at in return. I mentioned it again and they tried it properly for about 3 seconds and then plainly found it too difficult and so returned back to doing it poorly again. I should say this class was not my own so I had to tread carefully just in case I upset the person too much and I lost the instructor a student.

Perhaps I am just too hard, too much of a perfectionist, stupid, difficult, not very forgiving or actually just like doing things for a purpose. My advice, is do the exercises correctly to actually get some benefit from them.

Rant over.

Comments Welcome.

PS. My legs are still quite wobbily.