I'm going to refuse to give my friend his money back for a bet he lost
Oh really? Why would he not honor the bet you've made?
Because I'm a bad and greedy person and I want to keep it all for myself.
To be fair, your friend lost the bet fair and square. You aren't a bad and greedy person because you wanted to hold to the terms of the bet.
Yeah, that's what I'm saying.
He shouldn't even be asking for money back, he should just accept that he lost and move on.