Act/play the giddy goat
To act or play the giddy goat is to clown around or play the fool in a boisterous manner and dates in this sense from the late 19th century. The word giddy itself, however, is very old and dates from Anglo-Saxon times. It derives from the Old German gudo for god. Thus, a person who was giddy was thought to be mad or possessed, but in a godly or sainted without any evil or sinister connotations. The word ‘good’ stems from the same source. Thus, giddy was used to describe any form of agitated, possessed or boisterous behaviour. From the late 14th/early 15th century onwards, the meaning of giddy evolved to mean light-headed, as in experiencing dizziness or vertigo, and this is the meaning that is most often used today. Shakespeare used the word giddy 38 times in his works and, depending on the context, he used it to mean mad, possessed, frivolous or dizzy. To act or play the giddy goat only came much later, during the 19th century, when people were often deemed to play ‘the giddy ox’ as well as the giddy goat. In fact to play or act the giddy ox pre-dates the goat version but the latter seems to have stuck until the present day purely because of the alliteration. Along with the expression my giddy aunt, these are the only two expressions in English to retain the older and now archaic meaning.