How about I publicly support my friends relationship, but secretly hope that it implodes.
I hope you're joking about wanting your friends relationship to implode.
I would do anything to spite an ex-friend who has broken us up in the past.
You shouldn't wish for your friend's relationship to fail. You should be honest about how you feel about it and not be fake. It won't help maintain your relationship in a healthy way.
I'm an asshole, what did you expect?
Do you want everyone to know that you are an asshole? That's what will happen if you continue trying to wish bad luck on people and their relationships, especially friends that you're supposed to care about.