Rory has tended to think of her grandmother as the more difficult and exacting grandparent, while her grandfather can be counted on to dote on her. Moreover, her grandmother had a meltdown after Rory and Dean stayed out late together.
However, at the special dinner it is Emily who makes an effort to be civil with Dean (we already know from Rory’s Birthday Parties that she thinks social occasions are not suitable times to get into arguments), while Richard basically attacks Dean.
Richard is furious that his precious beautiful granddaughter, so smart and ambitious, bound for an Ivy League university and a glittering career, should have a boyfriend like Dean – an average student who doesn’t know where he’s going to college, and hasn’t thought about what job he might do later.
Richard comes down hard on Rory for choosing Dean as her boyfriend, telling her that as a Gilmore, she has a responsibility to uphold the family name. We know from his fight with Lorelai in Christopher Returns that the Gilmore name is very important to Richard, and that he has immense family pride. He warns Rory that Dean can only hold her back in life.
Richard is incredibly rude and snobbish in this episode, revealing how elitist he is. There must surely be some jealousy as well, knowing that he is not the most important male in Rory’s life.
Rory is justifiably angry with him, and defends Dean as well as she can – as she can’t exactly counter Richard’s arguments, all she can say is that Dean is incredible and special to her, and that he shouldn’t be treated that way as a guest before storming out.
Rory will later find herself in the same position as Dean when a future boyfriend’s parents don’t believe she is good enough for their son.