Perish the thought
Definition 1 of 1
Pro Tip 1/3Strong Rejection
Expresses that you really don't want something to happen or believe it shouldn't. 
Move to the city? Perish the thought, I love the countryside!
Pro Tip 2/3Not Serious
It can be used humorously to strongly reject something that's not likely to occur. 
Me, wake up before sunrise? Perish the thought!
Pro Tip 3/3Informal Settings
It's used in casual conversation. Avoid using it in formal or serious situations. 
Give up coffee? Perish the thought!