I'm going to take a pic of my friends fiances
Why do you want to take a picture of them?
I want to piss off my friend. He deserves it.
You shouldn't take pictures of people without their permission. Your friend and his fiancee won't appreciate that if they notice and might be upset with you.
They understand that I will do it every time they are with me.
There won't be other times if you continue to act this way. Your friend will stop being your friend.