piece of junk; worn-out thing
Refers to a broken-down, useless object, often a machine or vehicle. Colloquial and slightly derogatory.
このパソコンはもうポンコツだ。
This computer is a piece of junk now.
na-adjective, noun which may take the genitive case particle 'no'
This car has become a piece of junk now.
Describes a person or thing that is unreliable, incompetent, or not functioning properly. Often used in a self-deprecating or teasing way.
あの選手は最近ポンコツだね。
That player has been useless lately.
私って本当にポンコツで、すぐ忘れちゃう。
I'm really no good; I forget things right away.
dismantled car; scrapped vehicle
Specifically a car that has been taken apart for parts or scrap. A specialized use within the junk sense.
このポンコツから使える部品を取ろう。
Let's take usable parts from this dismantled car.
Dated slang for a punch or hitting someone. Rarely used in modern Japanese.
昔の不良はポンコツをくらわすなんて言ったらしい。
Apparently old-time delinquents used to say things like 'give 'em a punch'.
When it comes to operating machines, I'm hopeless.
He keeps driving his beat-up old car with care.
役立たず bluntly means 'useless person/thing' with a harsher tone, whereas ポンコツ is softer and often used self-deprecatingly or teasingly.
新品 means a brand-new item, the opposite of ポンコツ's sense of a worn-out, broken-down thing.
拳骨 (げんこつ, 'fist') sounds similar to ポンコツ and shares its old slang meaning of hitting someone, but 拳骨 is the standard word for a clenched fist while ポンコツ's punch sense is dated slang.
Katakana spelling is standard for this colloquial term.
Hiragana spelling is also used, especially in casual writing.
The exact origin is uncertain. It may be related to the sound of something breaking or being struck, but there is no clear historical derivation.