I googled around for an answer to your question.
Here's what I found from here.
"Sack the juggler - Said whenever anybody drops anything"
From another thread, same source:
"1.Upon hearing someone in a bar/restaurant dropping glasses or crockery -
"Sack the juggler!" "
Unfortunately, I couldn't find any "official" source.
I couldn't find an explanation as to the origin of the word either.
Hope this helps.