不请自来 uninvited
Explanation
不用邀请，自己前来。通常指不速之客，有时也指主动帮忙的人。
Coming without an invitation. Usually refers to uninvited guests, sometimes also to someone who offers help spontaneously.
Origin Story
话说唐朝时期，有一位名叫李白的诗人，他与贺知章相识，贺知章非常欣赏李白的才华。一日，李白听说贺知章在洛阳，便不请自来，去拜访他。他来到贺知章府邸，门房见是一位衣着朴素的年轻人，便想将他拦下，但李白执意要见贺知章。门房无奈，只好通报。贺知章听说李白来了，十分高兴，立刻出门迎接。两人在书房畅谈诗文，相谈甚欢。此后，两人结为莫逆之交，经常互相唱和，共同创作了许多流传千古的诗篇。
It is said that during the Tang Dynasty, there was a poet named Li Bai who knew He Zhizhang, and He Zhizhang greatly appreciated Li Bai's talent. One day, Li Bai heard that He Zhizhang was in Luoyang, and he came uninvited to visit him. When he arrived at He Zhizhang's residence, the gatekeeper wanted to turn away a young man in simple clothes, but Li Bai insisted on seeing He Zhizhang. The gatekeeper had no choice but to inform him. When He Zhizhang heard that Li Bai had come, he was very happy and immediately went out to greet him. The two chatted happily in the study about poetry and literature. Afterwards, the two became close friends, often singing to each other and creating many poems that have been passed down through the ages.
Usage
作谓语、定语；用于人和事物的往来。
Predicate, attributive; used for the interaction of people and things.
Examples
-
他竟然不请自来，打乱了我的计划。
tā jìngrán bù qǐng zì lái, dǎluànle wǒ de jìhuà
He just showed up uninvited and messed up my plans.
-
会议还没开始，他就已经不请自来，坐在了主席台上。
huìyì hái méi kāishǐ, tā jiù yǐjīng bù qǐng zì lái, zuò zài le zhǔxí tái shàng
Before the meeting even started, he came uninvited and sat on the chairman's platform.