disturber

from WordNet (r) 3.0 (2006)

disturber
    n 1: a troubler who interrupts or interferes with peace and
         quiet; someone who causes disorder and commotion

from The Collaborative International Dictionary of English v.0.48

Disturber \Dis*turb"er\, n. [Cf. OF. destorbeor.]
   1. One who, or that which, disturbs of disquiets; a violator
      of peace; a troubler.
      [1913 Webster]

            A needless disturber of the peace of God's church
            and an author of dissension.          --Hooker.
      [1913 Webster]

   2. (Law) One who interrupts or incommodes another in the
      peaceable enjoyment of his right.
      [1913 Webster]