What you might say in awe, disgust, or general surprise to someone claiming to have just done something stupid/not donesomething important. Usually shouted, often with emphasis on the "what".
"Sorry mate, there's rubbish all over the garden, it's because I forgot to tie up the bin bags"
"You fucking WHAT?"
MY FUCKING CAT IS A TERM FOR MY STUPID MOTHERFUCKING CAT THAT SCRATCHES AND MEOWS AT MY FUCKING DOOR AT 3 IN THE MORNING AND WHEN I LET HER IN 5 MINS LATER SHE DOES THE SAME THING TO GET OUT OF MY FUCKING ROOM.
"MY FUCKING CAT TASTES LIKE BURNT ORANGE CHICKEN FRIED IN GORILLA PISS"