Say your friend, a fellow trader, approaches you and says "I have discovered the holy grail - I never lose - I win every trade".... What do you say? Is there a polite way to tell him that he's full of shit and that you dont believe him?
Instead of being rude (you did say he is a friend)... Why can't you just ask him to show you in front of your own two eyes. In other words, go over to his house and watch him trade. If every trade is profitable that day...revisit him again and so on. If he continues to be profitable on every trade. You may get lucky into getting a glimpse of what he's doing without having to ask nor without being rude. However, if you meant as in an online friend... Ask for PnL statements (ones that show the details of each trade) especially if he's consistent in telling you that he is profitable on every trade. If he's not a friend...I guess its ok to challenge him, call him names, make demands et cetera. Mark