I'm going to set my friend up on a date in front of his ex
What's your friend's relationship with his ex?
He wants to date her again after breaking up
It seems like doing this will make your friend upset. Doing this knowing he wants to get back with his ex will enrage him.
I can handle whatever happens. My friend knows that I don't like his ex
Why are you willing to ruin your friendship over his ex? He will stop you from doing it and stop being your friend. Nothing bad would happen to his ex anyway.