The opposite of hooking up, characterized by a noticeable lack of intimate touching, lack of goosebumps and or chills, excessive amount of spooning and pillow talk, and occasional frumpiness. In terms of sexual baseballnomenclature, it would be considered a bunt.
Christian: "Did my eyes deceive me, or did I see Andrew hooking up with that girl from Iowa!"
Derek: "You are indeed mistaken sir, she is far too sober. Those two are definitely hooking down tonight"