A clusterfuck is someone who's a complete idiot. It can be used as a way to refer to your friends (as a joke), or to someone who's a total asshole.
"My friend can be a bit of a clusterfuck sometimes, but she's still the shit
"Man, that Abby bitch
is a total clusterfuck."
"God damn, Jason is such a clusterfuck... I'd love to shove my foot right up his ass."