To “Fuk Up “ - is to admit failure / unsatisfactory result of task / Kiss your friends Girl , forget to book a Taxi home etc.
When two or three “Fuk up's” manifest in succession or to “Fuk Up” which may result in previously uncharted levels of a displeasure – you will know when a “Clusterfuk” has occurred.
Other such examples of a “Clusterfuk” - Hitler's invasion of Russia in winter. Napoleons invasion of Russia in winter. Shagging your best friends wife , thus ending a life long relationship with him and indeed your close family circle. Getting caught doing something that may result in 3- 5 years prison time. Getting drunk and joining the Army. Being unfortunate enough to have been born in Ireland.