Green’s Dictionary of Slang

(US milit.) surpassing all previous fuck-ups.

1955		S.V. Baum ‘From “Awol” to “Veep”’ in AS XXX:2 103–4: Derivative terms reported in popularity among government workers included [...] sapfu (’surpassing all previous foul-ups’).
2001		S. Dutch ‘Printing’ on University of Wisconsin 🌐 These were just a few of a host of World War II acronyms, including: sapfu: surpassing all previous f***-ups.