Hooking Down is when you hook up with someone below your social grade, be it in looks, popularity or overall personality. Hook downs are generally done due to uncontrollable horniess, rebounds, depression or revenge.
"James could get with anyone in school he wants, why is he hooking down with her?"
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"
To hook up with someone of lower social status and/or attractiveness level.
(A few girls are looking at facebook)
"Ew, that guy is so fugly"
"OMG. him and I were hooking down last night at the club"