Definition
This idiom is used to tell someone off for not paying attention or for saying something nonsensical.
注意力不集中嗎！
What you just said makes absolutely no sense, you should just go back to sleep!
你剛才說的話完全沒有道理，你應該回去睡覺！
He kept dozing off in class, and the teacher told him, "You might as well go back to sleep!"
他在課堂上一直打瞌睡，老師對他說：「你不如回去睡覺吧！」
Don't ask me, you weren't even listening to me, go back to sleep.
別問我，你甚至沒在聽我說話，回去睡覺吧。