I was watching 賭場風雲 (Dicey Business) and 25 came into talk. Usually I don’t think much when they call people 二五仔 (literally means 2,5 person, but is slang for a snitch or traitor).
Anyway, they drugged this poor guy and started painting 25s on his face and body, and my sister asked me what’s 25. I told her it referred to 二五仔 because they believed he snitched on them. Then my sister asked me why 25 referred to a snitcher and I had no idea. At first I thought maybe it was because it’s easier to write instead of 厭仔, but it turns out there’s not such a phrase.
I asked my dad and he believes it refered to 2 5’s which is the number of fingers on your hand. People who snitch are like finger pointers. I decided to search for the phrase online to see if I could find the origin and I found these 2 links:
至於「二五仔」則是出自一個坊間盛傳的故事，話說清朝年代，少林寺有一百零八位武僧，一名叫馬寧的，因犯事而被主持逐出少林寺，他懷恨在心，竟走到官府告密，透露少林寺的保安機密資料，包括洩露有民間反清份子為避官兵的追捕，逃入少林寺假扮僧侶，馬寧並帶領官兵火燒少林寺，追捕欽犯。有說法指馬寧是百多位武僧中輩份排行第七，另一則說他的武功之高是眾僧中排第七，結果，江湖中人便以馬寧出賣少林寺一事，將「七」字分拆為「二五」，再諷剌地叫他「二五仔」，並以「二五仔」統稱出賣兄弟者。
「二五」代表的其實是它們的總和—-「七」。故事須從火燒少林寺說起︰話說清朝康、雍年間，朝廷要徹底消滅反清復明的秘密會社，查得少林寺與天地會有千絲萬縷的關係，於是派兵前往剿滅。但需要有少林寺內奸策應，所以收買了武功排名第七的少林俗家弟子馬寧兒。馬寧兒窮凶極惡，犯下大罪，被逐出山門，含恨引清兵入山，火燒少林寺。秘密會社中人不恥其所為，日後便稱那些告密者、叛徒為二五仔 (指排第七的馬寧兒)。
According to the sources, 25 refers to the sum of its digits: 7.
During the Qing dynasty, there was a group of people called 天地會 (Heaven Earth Group) that wanted to overthrow the Qing Dynasty and restored the Ming Dynasty. They were quite intertwined with the Shaolin temple. There was a monk in Shaolin named 馬寧 (Ma Ling) and he was exiled from the temple for commiting a crime. With hatred in his heart, he went to the government and snithced on the Shaolin temple and how they were hiding fugitives and the connections that they had with 天地會. The government sent an army and burned down the temple and from that day on, 馬寧 was known as a traitor. There were a total of 108 monks and they were ranked. 馬寧 was ranked number 7 and from that we have 二五仔 which is a Cantonese slang for snitch/traitor.