Noun: The opposite of "mea culpa," Latin for an act or omission that is "my fault". A "you-a-culpa" is an act or omission that is all YOUR fault and not at all MY fault.
Usually associated with a complex situation where the appropriate person or persons to blame is open to dispute.
When the house fell down shortly after contruction, all the you-a-culpas started flying.
Don't start with the you-a-culpas, man. I know you're the one who wrecked my transmission!