开口要有礼貌，不讲下流话。

One must be respectful when speaking, and not say obscene things.

Source: Tatoeba

Sentence Composition

1 开口 kāikǒu
  1. to open one's mouth
  2. to start to talk
2 要有 yàoyǒu
  1. to need
  2. to require
  3. must have
3 礼貌 lǐmào
  1. courtesy; politeness; manners
  2. courteous; polite
4 不 bù
  1. no; not so
  2. (bound form) not; un-
5 讲 jiǎng
  1. to speak
  2. to explain
  3. to negotiate
  4. to emphasize
  5. to be particular about
  6. as far as sth is concerned
  7. speech
  8. lecture
6 下流 xiàliú
  1. lower course of a river
  2. low-class
  3. mean and lowly
  4. vulgar
  5. obscene
=7 话 huà
  1. dialect
  2. language
  3. spoken words
  4. speech
  5. talk
  6. words
  7. conversation
  8. what sb said

classifiers: 種, 席, 句, 口, 番
=7 话 huà old variant of 話 huà