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 baseball nomenclature, 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"