Why cause harm to someone ?? I tell them that it is the most difficult line of work that I have ever come across (and I have had quite a few changes of career in my 52 years) and that 7 years down the line I am still not at matriculate level. Of course, they don't believe you, but the 2-3 times that I have let someone sit next to me and watch the screen, they find the charts and price movements interesting at first, and then scary after 15-20 minutes
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Then there are those who will sit next to you and egg you to trade "Buy this, looks like it will go 10% high", or even more laughable "Buy this, it will go up because I am saying so". In such cases I just say "Ok, deposit 20000 Rs. advance with me to cover the losses if they happen, and I'll take the trade. If there is any profit, I'll give it all to you". That scares them. It's ok for the others to comment as long as their money is not involved. So if I find someone becoming a pest about it, I bring the topic to involving their money.
There's not much one can do about those who call it gambling or "doing nothing productive" etc. So I avoid those.