A handjob, usually given out of a feeling of guilt for almost boning someone before changing one's mind. Made popular by UCSB student Rose, whose reputation for giving rosies to the drunken boys of Isla Vista is unmatched.
Says Rose of rosies, "They're just like saying hello. They mean nothing to me."
I was surprised when Jake whipped his dick out, even though we had extensively grinded at the party and dry-humped on my bed. By the rules of UCSB, I was pretty much obliged to give him a rosie.