原谅我人不好嘴不甜
[yuán liàng wŏ rén bù hăo zuĭ bù tián]
This nickname means “Please forgive me for being mean and not very flattering”. It's often used when someone is aware they're a bit grumpy or harsh. But it also contains a humorous undertone since this type of negative intro makes people think they will behave more nicely than described after seeing these honest but negative traits first.