Pretty close actually I think, based on being wicked stepmother to an 11 year old and having two younger brothers. I've never heard anyone that age use 'prick' though, not ever. 'Dick' would be for being crude (to your friends, maybe in his own mind - little boys are *very* fond of that word!), and 'willy' for being more coy / talking to parents probably. I could see Petunia making up some god awful word though to avoid Dudley using anything remotely rude *g*