Fucken A is a word that some people use when they are stumped on something and to indirectly say the word Fuck.
"this is so Fucken A"
Aknowledgment with a companion that the event, subject matter or suggestion presented is as good if not better than the original discription.
John: You wanna go get a hooker!
Jack: Fucken A!
Billy finds $20 on the ground, "Fucken A!"