I think we would be wise to never use the term "vegetable" to refer to human beings. First, no vegetables ever have souls - all humans do, regardless of their physical condition. Second, use of the term implies a less-than-human existence in which those who hate life are quick to glob on to in order to legitimize the murder of such persons.
Point taken.
But, if my earthen vessel (body) should ever become truly vegetative, I couldn't care less. Feel free to refer to it that way. By definition, there won't be any life remaining in it for anyone to hate, because my soul will have already left the scene. Life-haters, "glob" away! ;O)