User blog comment:Chawk1993/Favourite Merlin Insults/@comment-4999494-20120509172534/@comment-4062486-20120509175712

I'm not 100% sure myself what it exactly means. I do have an assumption though: since one of the meanings of the word "dollop" means a small quantity, dollop head may indicate that Merlin thinks that his head (which in this case most likely means mind) is small, which means that he thinks Arthur is stupid.