Meaning:

“毒” means “poisonous,” and “奶” means “milk.” The character “奶” as a noun is often used by gamers to refer to the profession of curing warriors in games. When used as a verb, it means to “cure injured warriors.” “Poisonous milk,” therefore, refers to the action of injuring one’s teammates instead of curing them. Gamers also use the term to generally mean someone is a “jinx.”

Example:

A: 我觉得明天我们比赛一定会赢。

Wǒ juédé míngtiān wǒmen bǐsài yīdìng huì yíng。

I feel certain we will win tomorrow.

B: 还是别夸口了，小心输了被大家骂你是毒奶。

Háishì bié kuākǒu le，xiǎoxīn shū le bèi dàjiā mà nǐ shì dúnǎi。

You’d better not boast. If we lose, people will call you a jinx.