When something happens higgledy-piggledy, it's chaotic and disorganized. If you build your Lego tower higgledy-piggledy, it may end up too tall and narrow, making it that much easier for you brother to knock it over.
You can use this word, known as a "reduplicated phrase" for the rhyming repetition of its sounds, as an adjective and an adverb. So your dad may object to the higgledy-piggledy state of your room, and you might respond by throwing everything higgledy-piggledy into your closet. It's a great word that perfectly illustrates disorder or confusion. Unlike other reduplicated phrases such as hanky-panky or helter-skelter, higgledy-piggledy is a rare double dactyl, a repeated three-syllable word that stresses the first syllable.