I think you could highlight jhsph07's discussion about penny stocks. Change the title into never use more than 5% of your money into one penny stock.
some senior traders said that if they could go back several years ago, they would like to start with penny stock because sometimes penny stocks were not as volitile as options while sometimes independent with overall market, which made them one of the good tools to make money.
The key is never use too much money into one.
Remind all the newibes and highlight the warning. That is all.