chickened out, backed out, deflated, coward, wimp
Il s'est dégonflé et en a laissé une.
He chickened out and left one behind.
— La piel que habito (2011)
Je devais aller chez le dentiste et je me suis dégonflé.
I was supposed to go to the dentist, but I chickened out.
— The Tall Blond Man with One Black Shoe (1972)
I didn't chicken out.
Il s'est dégonflé au dernier moment.
He backed out at the last minute.
Je suis un dégonflé, par rapport à toi.
I'm a wimp compared to you.
Tu t'attendais à un matelas dégonflé ?
Were you expecting a deflated mattress?
— The Big Sick (2017)
The tire is a little deflated.
Tom a dû pousser sa bicyclette aujourd'hui car il avait un pneu dégonflé.
Tom had to push his bicycle today because he had a flat tire.