3 sentences

1. “老外”是对外国人的俗称。

   “ lǎo​wài” shì duì wài​guó​rén de sú​chēng.

   'Laowai' is a common nickname for foreigners.

   Source: Dong Chinese Dictionary

2. 那个老外会说一口流利的汉语。

   nà gè lǎo​wài huì shuō yī kǒu liú​lì de Hàn​yǔ.

   That foreigner speaks fluent Mandarin.

   Source: Dong Chinese Dictionary

3. 谈到核物理，我可是个老外。

   tán​dào hé​wù​lǐ, wǒ kě​shì gè lǎo​wài.

   When it comes to nuclear physics, I'm a complete layman.

   Source: Dong Chinese Dictionary