Peter lumps murderers, thieves, evil doers, and busybodies all into one category. How bad is it, really, to be a meddler or a busybody compared to knifing somebody, robbing them on the road, or just being downright evil? What is so bad about busybodies? Why does the Bible take such a stern view of meddling?
The New King James puts the word "meddler" in the margin—a very good translation of this word. The Greek word translated "busybody" or "meddler" is allotriepiskopos, a compound word—two normal Greek words stuck together—found in the Bible only in this one spot.
Allotriepiskopos literally means "not one's own overseer." "Not one's own" is one word and "overseer" is the other. It means, thus, "one who oversees others' matters or affairs." This word contains episkopos, which is the Greek word for "overseer," sometimes translated as "shepherd" or "bishop." This allotriepiskopos could be a good thing—if it was someone like a steward of an estate who was assigned to be the caretaker of another's matters, or an executor of a will, someone who is appointed to look over another's affairs after his decease.
However, in this one occurrence and in the normal Greek (it is used only a couple of other times in the classics and not quite in this same context), it is a negative term. It describes a person who takes it upon himself to interfere in another person's matter.