Someone who has no backbone or gonads, totally unable to think for himself and therefore takes direction from someone else. Thus, he is a pillow and bares the imprint of the last ass that sat on him..
My ex-best friend is a pillow. His new girlfriend doesn't like me, so he threw away our friendship because she told him to do it.
n. A rectangular cloth bag stuffed with feathers, foam rubber, or other soft materials, used to support the head when lying down.
v. Rest (one's head) as if on a pillow.
(OED)
ed. - Also a brilliant tool to engage in friendly fights in. Honestly, people.