- Take someone out of his/her misery: ajudar
You don't know how to solve this! No worries, I'll take you out of your misery.
- Be puzzled by something: confuso ou intrigado.
I am puzzled by what you've said to me!
- To go off the rails: perder o controle de algo, sair dos trilhos
Certainly she can't drink that much, after 2 pints she already goes off the rails.
- Had better: como um conselho, dizemos que algo eh melhor para alguém
You're ill today, you'd better go home.
- Be over the moon: muito feliz
When they told me I had passed the test, I was over the moon