2 sentences for 马甲 (mǎ​jiǎ)

1. 他在衬衫外面套了一件黑色的马甲。

   tā zài chèn​shān wài​miàn tào le yī jiàn hēi​sè de mǎ​jiǎ.

   He wore a black vest over his shirt.

   Source: Dong Chinese Dictionary

2. 那个博主为了给自己带节奏，开了好几个马甲。

   nà​gè bó​zhǔ wèi​le gěi zì​jǐ dài​jié​zòu, kāi le hǎo​jǐ gě mǎ​jiǎ.

   That blogger created several sockpuppet accounts to manipulate public opinion.

   Source: Dong Chinese Dictionary