イギリスの家庭でホームステイをしていた1980年代後半、毎週日曜日にBBC１で放映されていた「East Enders」というドラマがありました。ロンドンの下町に住む人たちの日々の出来事を描いた「メロドラマ」に近い番組でした。地元の人々が仕事が終わると、’Queen Victoria’ というパブに皆が立ち寄って、いろいろな情報交換やゴシップをするシーンが良く出てきていました。人間、お酒が入ってついつい余計なことを口走ったりすると、誰かと口論になることもあります。パブの中でも、昔の事件や喧嘩のことを根に持っている人が、機会を捉えては口論になることもありました。または、完全な誤解が原因で、誰かと取っ組み合いの喧嘩（けんか）になることもありました。喧嘩（けんか）の最中や一段落したシーンで、’He has a chip on his shoulder. Do not take any notice of him.’ などの台詞が出てきたのを記憶しています。
I was staying with an English family in Kent in the late 80s. On every Sunday afternoon, while we were having a hearty Sunday lunch, we all watched ‘East Enders’ on BBC One. In those days, it was one of the most popular soap operas in the UK. The programme featured the day-to-day social life of the people living in the east end of London. The local people made a habit of stopping by the ‘Queen Vic’ (well, that how they called the pub anyway) where they met their friends or aquaintances and caught up with their latest news or just had some chats with each other. When you are toxicated, you could easily got carried away and say something silly to someone which you regret afterwards. Similar things happened during the programme(s) where two parties started to have a quarrel over something trivial. At the Queen Vic, people started a quarrel out of the grudge from the past incident(s) or fight(s) between the parties involved, or out of an utter misunderstanding over something. Sometimes, the quarrel developed into a serious fight inside or outside the pub. In the middle of the fight or after the fight, onlookers around the fighers often said to one of the parties involved, ‘He has a chip on his shoulder. Do not take any notice of him.’ That is more or less how I remember coming a contact with this expression.
PS-Mind you, initially the Cockney accent was so hard to understand because they drop every ‘h’ sound in their English speech! Furthermore, the voiced ‘th’ sound is pronunced as ‘v’ sound. So an English word ‘another’ actually sounds like ‘anover’, or ‘mother’ sounds like ‘mover’! However, in the end, I more or less overcome this accent problem, and started to enjoy the programme. Spending a lot of time in front of a ‘telly’ did me a good education on the typical accents of British English. Now I can recognise the following varieties of English: Welsh English, Scottish English, Rhotic accent in Devon and Cornwall area, Kentish accent, Yorkshire accent, Irish accent, Standard English accent, Hyperlect (an accent heard with some people from an upper class family). Outside Britain, I can recognise Australian accent as well as American accent.
‘Chip’ in this expression means ‘a small piece of wood’. I have hearｄ that this idiom has the following origin: in days gone by in America, one of the parties involved with the fight put a chip on his shoulder and provoked the other party to knock it off at the risk of being punched back.
今では、何か瑣末なことがきっかけで、妙にふてくされた態度や、嫌悪感をあからさまにして「喧嘩腰」になっている人、劣等感やひがみなどから挑発的になっている人に対して用いられます。大したことでもないのに、相手が喧嘩腰になってきたら、使ってみましょう。私の持っているDVDバージョンのコーパス—BNC （British National Corpus）—には、以下の例が載っていました。
Now ‘a chip on his/her shoulder’ is used for someone who meets the following criterion: being sulky, provocative because of a grudge or an inferiority complex. So if someone becomes nasty to you and dares to have a fight, you could say to him/her, ‘You have a chip on your shoulder’. On the DVD edition of British National Corpus (BNC), I have come across the following example.
‘He had a bit of a chip on his shoulder because he felt that other people who were not so good but who had the right background and connections had gotten ahead of him.’