不要隨便開玩笑。

Stop fooling around.

Stop joking around.

Source: Tatoeba

Sentence Composition

1 不要 bùyào don't!; must not
2 隨便 suíbiàn
  1. as one wishes
  2. as one pleases
  3. at random
  4. negligent
  5. casual
  6. wanton
3 開玩笑 kāiwánxiào to play a joke; to make fun of; to joke