Social media users use words and phrases to convey their views or opinions. However, some people use idioms or proverbs that are implicit and indirect to make a stronger impression on the audience or perhaps catch their attention by utilizing funny, sarcastic, or metaphorical phrases. Idioms and proverbs are figurative expressions with a thematically coherent totality that cannot be understood literally. In previous work, the extension of IBM's Sentiment Lexicon of Idiomatic Expressions was proposed to include around 9,000 idioms; a crowdsourcing service manually annotates both lexicons. Therefore, in this research, we provide a knowledge-based expansion approach to avoid human annotation of idioms. For sentiment classification, the proposed method has the advantage that it does not require any fine-tuning for the BERT model. Experimental comparisons show that automated idiom enrichment and annotation are very beneficial for the performance of the sentiment classifier. The expanded annotated lexicon will be made available to the general public. © 2013 IEEE.