Examples from literature

• A fellow may be a duffer generally and yet turn out Latin verse better than fellows who are vastly superior to him on other points. 
• At the end of three weeks I was still a duffer. 
• But this chap's a regular duffer! 
• He will be terribly upset, but, you know, the dear old duffer really loves me. 
• Perhaps I'm as much a duffer in music as in other things. 
• That is one of the symptoms of the golf duffer.