Get one’s dander up

To get one’s dander up means to get angry or annoyed. The expression is American from the early 19th century. Dander, which the OED says is an alternative of dunder, was the name for the froth that forms during the fermentation process, deriving from the Spanish redundar meaning to overflow. During the 18th century, it was a word commonly used in the molasses industry in America. When anything ferments, it gets agitated and froths up, providing an apt metaphor for getting angry. See also Get in a froth.