Can be said in good or bad context to indicate a positive or negative reaction (respectively), but no matter how it's used... it still means "Fuckin' Awesome"
-Fuckin A, man!
2)Fuckin A, I can't believe I won.
3)Fuckin' A!... somebody finally wrote a decent definition for "fuckin' A"
This is the correct spelling - beware the overformal 'fucking a', taking time to pronounce the g is a profanity faux pas and de-emphasizes the strong expression of agreement - you might as well say "jolly good show", queerbait.
Also beware dropping the apostrophe for the omitted g, just because we're using profanity doesn't mean we need to do it like an illiterate.
Hudson - "Fuckin' A..."