*spoiler alert* If you have not watched Memory Lost Season 3 Ep 1 yet, its probably best for you to read this with caution as there may be spoilers ahead*
During Season 3 Ep 1, Han Chen had invited all the members of the Black Shield Team for dinner at an expensive restaurant and offering to pay for the bill. Because of the prices of the dishes, both Xiao Zhuan and Prate were a little worried about ordering. Han Chen reassures them by saying it is not a 鸿门宴/ pinyin “hóngményàn”. It is a term commonly used to describe a meal, with an ulterior motive behind it, often a bad one. ( I guess the subtitle wasn’t 100% accurate but I didn’t have the space to explain it well.)
The phrase comes from a true historical event at the end of the Qin dynasty around 206 B.C. Around this time, there were many different powers vying to become the next Emperor of a united China, one of them was Xiang Yu 项羽 and the other Liu Bang 刘邦 who had worked together to overthrow the Emperor. It was a meeting to agree upon how China would be ruled after the fall of the Qin dynasty. Although Liu Bang had entered the capital of the Qin dynasty first, instead of plundering all the goods, when he heard of the news of how powerful an army Xiang Yu had, he retreated and waited for Xiang Yu to arrive.
The reason why it was called 鸿门宴 was because the banquet was located in a place called 鸿门. Before the banquet, the messenger Liu Bang had sent to Xiang Yu had tried to create a rift between Xiang Yu and Liu Bang. Also, a fortune teller had told Xiang Yu that Liu Bang had the aura of a king so he was advised by his ministers to kill Liu Bang. However Liu Bang found out about this plan through a minister who was friends with Xiang Yu’s uncle who had overheard the plan to kill Liu Bang. To try and lessen Xiang Yu’s anger, Liu Bang met with Xiang Yu’s uncle, Xiang Bo and offered marriage in exchange for Xiang Bo to persuade Xiang Yu to be civil towards him. This seemed to work, although Xiang Yu was still suspicious.
At the banquet, Liu Bang that is traditionally where the lowest ranking courtiers would sit, therefore suggesting to Xiang Yu wishes only to be his subject and serve him and not fight for his crown. Seeing this, Xiang Yu believed he would be a loyal subject and decided not to kill him.
The sword dance
Xiang Yu’s closest advisor, Fang When did not believe in Liu Bang, and throughout the banquet, signalled to Xiang Yu to order the death of Liu Bang, which his leader ignored. In desperation, Fan Zeng asked Xiang Zhuang, Xiang Yu’s cousin to perform a sword dance. Xiang Bo seeing this joined in and protected Liu Bang from Xiang Zhuang’s sword.
Escaping via the going to the bathroom/toilet excuse
It seems whether it was a thousand years before or now, whether you wish to escape from a boring party or from someone who wishes to kill you at a banquet, saying that you have to go to the bathroom, but instead run out of there using the back door, never gets old. Claiming that he needed the toilet, Liu Bang instead fled and handed some gifts for one of his men to give to Xiang Yu and Fan Zeng to apologise for leaving early.
Xiang Yu’s End
Unfortunately, in the end, it seemed Xiang Yu should have killed Liu Bang as he finally defeated by Liu Bang, committing suicide in the end. However Xiang Yu goes down as a bad ruler but a great military leader in chinese history due to his folishness and his inability to appreciate the good advisors he had who left him one by one to serve Liu Bang.
There is a chinese film called 鸿门宴/ White Vengeance which describes this event.
Also there is a chinese drama called 王的女人/Beauties of the Emperor which has an episode loosely based on this.