To have a strange fixation about something; to have an eccentric idea or fantasy. A version of the term appears in Robert Herrick’s “Mad Maid’s Song” (ca. 1648): “. . . the bee which bore my love away, I’ll seek him in your bonnet brave.” Allegedly the expression stems from the analogy of a bee buzzing inside one’s hat to a peculiar idea in one’s head. It has been a cliché since the eighteenth century. Lest one think it is obsolete, it appeared in a 2004 murder mystery: “By the way, what bee got into your bonnet at the meeting? Bailey had been pretty cooperative” (David Baldacci, Hour Game).