Bristle up is defined as a feeling of irritation or anger that causes a person's hair to stand on end. However, there are multiple synonyms that we can use to express this emotion efficiently. For instance, the phrase 'getting one's hackles up' can be utilized to convey the identical emotion. Other alternatives for bristle up include getting riled up, becoming annoyed, getting provoked, irritated, or incensed. The use of these synonyms allows us to communicate the same feeling with a more precise choice of words and to convey the intended message with greater effectiveness. Therefore, it is necessary to understand the synonyms of different words to communicate more effectively and accurately according to the context.