STUPID/NOT SENSIBLEsomeone who is stupid or not very good at something 笨蛋,无能的人
Examples from the Corpus
duffer• Oliver says he is a duffer, but keeps him on because he is so helpless and lonesome.• The agent's an awfulduffer when it comes to dates.• By refraining I have no doubt I shall receive the silentblessings of the multitude of duffers among whom I find myself.• I was never your prototypicalduffer.• I think a lot of people feel vaguely when they see two duffers marrying that the duffers must prefer it that way.
Originduffer
(1700-1800) Perhaps from Scottish Englishdoofart“stupid person”