How to remove method initialize./package methods

Have defined a new class (by setClass) and added a method initialize (setMethod("initialize"). 

setMethod("initialize"
          ,signature(.Object="Massvector")
          ,function(.Object,data,info,tcoor,gelcoor)

But I dont like it and want to remove it!

showMethods("initialize")

...
.Object = "Massvector"
    (inherited from .Object = "ANY")

removeMethod("initialize","Massvector")

[1] FALSE
Warning message: 
No method found for function "initialize" and signature "Massvector" in: removeMethod("initialize", "Massvector") 



How to remove it?

Eryk.