A person (tipically a woman) who masterbaits with a pillow.
Many people enjoy the softness of a pillow. Woman typically ride a pillow in the cowgirl position, while men may thrust in between two pillows.
The visual thumping and thrusting of a woman riding a pillow is where the "Bunny" part comes from.
She is such a Pillow Bunny, she only wants to make love on top of me!