別那麼正式 的英文怎麼說?

[1] Don't be so formal.[2] You can keep it casual.[3] Don't stand on ceremony.
  There is no need to stand on ceremony.[4] Make yourself at home.
  Make yourself comfortable.

Don't be so formal = You can keep it casual = 別那麼正式，也有「別太拘束」或「別太客氣」的意思。

其他的句子也很常用，例如 Make yourself at home. 就表示你把這當自己家，別太拘束或客氣。