I have been teaching for many years and have ran into this many times. when I demo something I expect that the student will come at me as hard as they can, so that I do not get cought off gaurd like this. Have I gotten cought YES and we all have. How to deal with it is the question. I never demo somthing that I can not get out of period. i use the approperiat amount of force needed to get out of it. when something like this happens I like to use it as a teaching experiance. normaly it is Obvious what the students intention was to the rest of the class. Now they know that is works. After the class you need to explain why that this should not happen. Then they are probation. They will only work with person of higher rank who will be informed of the situation or I like to work with them personally. The lesson will continue until I fell they have learned. Another approach it to do privet lessons with them. Then let them set the pace of the class. I have done this many times there has not been more then one or two lessons before they learn my ability and the dangers of unnecessary hostility. Another approach it to do privet lessons with them. Then let them set the pace of the class. I have done this many times there has not been more then one or two lessons before they learn my ability and the dangers of unnecessary hostility. We as instructors are just that. We must educate them. We are part friend, part counselor, and part teacher. Find out why they behave the way they do. Once this has been done the behavior is not normally difficult to change. Many students come to us to learn martial arts but it is up to us to also find out what they need on top of the physical curriculum. They pick martial arts over other avenue of help for a reason. What is it?