Answer:
   
   Some Jews consider Jesus to have been an ordinary man and write his
   name like that of any other man. Some question whether or not he even
   existed, possibly being a myth borrowed from similar stories. Others
   ascribe to him the status of a "deity worshipped by others," whose
   name Jews should not pronounce. Many extend this ban to the written
   form. Some write "Xianity" as a simple shorthand, like "Xmas," while
   others prefer not to write "Christianity" lest it appear that they
   consider Jesus to have been the Messiah.
   
   Note that the shorthands "Xianity" and "Xmas" do not derive from
   attempting to "blot out" the Jesus's name; rather, they arose because
   the first letter of the Christ in greek (Christos) is a Chi, which
   looks like an "X". In fact, the shorthand is used by many Christians.
   
   The possible halachic problem with writing Christ derives from the
   fact that "christos" is the Greek word for Messiah/moshiach. Hence
   some argue that writing the name Christ in full tacitly acknowledges
   (G-d forbid) that Jesus was the Messiah.