off the back of a lorry

Từ điển Oxford Advanced Learner 8th

off the ˌback of a ˈlorry f8 idiom
(BrE, informal, humorous)goods that fell off the back of a lorry were probably stolen. People say or accept that they came ‘off the back of a lorry ’ to avoid saying or asking where they really came from.
Main entry: ↑back_idiom