Harry potter and the half blood prince?

Sorry but you're all mistaken...Slughorn only favors those he feels important . He just doesn't bother to remember his name. Pg 397 on Ron's birthday when he's had the love potion spiked candy and needs the antidote from Slughorn ' "There you are then",said Slughorn, handing Harry and Ron a gl of mead each before raising his own. "Well, a very happy birthday, Ralph--" There's also one other name he uses instead of the correct one and I can't remember where!