Literal meaning is goose bumps. But when someone see a too much sweet couple or is jealous of them he(or she) say Oh ! 닭살 as a joke. It is a Korean style funny expression. .

sappy? as in sap? means either juice of a woody plant or body fluid. It can also be slang for someone who is a fool.

커플이 애정행동을 하면 질투가 날 때 하는 말이에요 If you love the couple acting mean to me when jealous....haha..