What is Ralph insinuating when he says "be sucking my thumb next"?

In the story "Lord of the Flies" the author, William Golding uses literary color to envelop the reader into the emotions and experiences of the boys on the Island.  The boys slowly see the social behaviors taught through civilization falling away.

The character of Ralph, is the good leader, who represtent the lessons one would hope that the other boys would continue to guide them as time progress on the island.  Ralph represents social order and stability in a strange and uncontrollable environment. 

While Ralph displays qualities of a good leader, he only identifies his weaknesses and is even more upset as his own appearance and cleanliness changes.  He is upset with the bizarre behavior of the other boys.  Because he can no keep himself together in the way he would like, he makes the statement ""Be sucking my thumb next" found on page 109 of the text.  He states this in response indicating that he is going backwards at not being able to care properly for himself and wonders how far he will regress.  He does not really think he will begin sucking his thumb but he uses it as a metaphor to show how badly circumstances have regressed.