Cranks are the citizens in the Scorch who are slowly going insane. Some Cranks are only half-crazy, like the ones Thomas meets at the party. These Cranks are able to function and think logically (sort of), but something is certainly not right with them. When Thomas refuses a drink from a Crank who has long hair, for example, the man says:
"I offered you a drink," Long Hair said again, the time any sign of kindness gone from his tattooed face. "It would be very rude to turn such an offer down." (37.37)
Hmm, what a nice guy.
Not only does Thomas characterize each Crank by their physical qualities, but most Cranks we encounter are totally unpredictable and even evil. They want to kill Thomas—or at least use him for something. Something is always just a little bit off with each of these people.
Then you have the full-blown Cranks, like Mr. Nose, who famously says: "Rose took my nose, I suppose" (31.46). What does that mean? Who knows. It's not really supposed to mean anything; it's just crazy. These people are just out-of-their-minds loony. Nothing they say really makes sense, and on top of that, they all act like zombies.
On the other hand, hey, they do have a pretty good sense of humor. Er, as long as "Rose took my nose, I suppose" is supposed to be a joke.