Add fuel to the fire
Angela: "I wanted to help, but I was afraid I would add fuel to the fire."
安吉拉：我想帮忙，但是我怕是在火上浇油。
A conflict between two people is like a fire, with both people adding "fuel" to the fire. You add fuel to the fire when you do something that makes the conflict worse.
中文意思：火上浇油。
When pigs fly
Angela: "Do you think you will ever work at that company again?"
Andy: "When pigs fly!"
安吉拉：你认为你还会在那个公司工作吗？
安 迪：绝对不可能！
When pigs fly is an informal way to joke that you will never do something.
中文意思：永无可能。