My advice: try to talk jokingly to them, saying something like:
"Yeah, that story sounds cool, don't we all like to be winners,
and showing them that we are better, smarter etc. ...
But honestly, do you really want to be a revengeful person ?
Really, really, do you want to be that ?
I myself do not want to be such a person.
I want to be a person who is fair, truthful, integer,
and I believe if I am such a person, then I will be respected."
In terms of the overall effects: you will not know the outcome.
That person can actually decide to really become a revengeful person,
and it's his own choice then. You just pointed out to him,
that it is his freedom/conscious decision to be such a person.
The outcome may also be, that your friends start think
about their attitude.
But frankly speaking: it sounds as if you are the doormat
of your friends, having to listen to their needs
and not being able to express yourself (at the cost of loosing
a friendship)
with best intentions
Wolfgang