The problem of the silent cemetery(sample bias?). If we start with a large enough cohort of "equally skilled" traders, who just make their investment by random, we will still end up with a handful of "old foxes" who just standing because of their proportional luck. In the meantime the failed ones laying in the cemetery silently as nobody asks them.
Of course the lucky one's skills will be rationalized(narrative fallacy in Taleb's term) and not just by themselves but the majority around them, the media etc..
A sneaky move would be to do something like: "I don't know, umm yeah.. thinking about it from this viewpoint it would be interesting if .. " and suddenly listing previously not said(and usually more tangential) arguments going against your previous argument and supporting your pal's statement. The point is that you somewhat start to act like a judge of your own discussion, accumulating even more status retaining control and the image of a reasonable man.
Completely steal the show. Although it usually works only with one person dialogues, if others are present they would assure your puzzled pal that the credit indeed belongs to him ,)
Another good flip(or reframing) would be "ohh yeah let's continue just for the sake of the argument, to see how far this point could be derived" than defend it with your original intention. If works you have it, if not it's not attached to you anymore.
But sometimes you just feel the insignificance to the universe and let it go with a smile.