Trying to think of a Phillie I hate the most was actually harder than I had anticipated. I'm ashamed to admit though that the last time I watched any Philly/Met game of any sort of significance was last season and therefore the Phillie I hate the most comes off last season's roster:
PAT BURRELL.
Pat Burrell has 42 HR and 104 RBIs lifetime versus the Mets. Thanks Pat. Thanks that you usually look like a fool and strike-out 12 times a game versus everyone else in the league but pound the Mets. Pat is a Met killer but deserves his Philly boos against everyone else. When the Mets roll into Citizen's Bank Park he's all of a sudden the most popular jersey in the place. I hate that he'd be a Hall of Famer if only ever played against my favorite New York squad. I hate that stupid picture of him working out like he's the coolest thing to ever walk on the earth

(small side note, I did enjoy WS parade Pat leading the way, riding on his Budweiser wagon being pulled by Clydesdales- saying to Philly, you didn't think I could ever bring you a ring, now I did, now I get to ride down Broad Street like I literally own the place, forget my teammates, give me my beer, pick up my horses' poop, and kiss my ring).
Burrell's slaughtering of the Mets is second only to the extremely hated LARRY (Atlanta's Chipper Jones). At least he appeared to be a class act, ran hard, kept his head down, and even named one of his kids Shea in respect of how much he loved to play there. Not much can be said about Pat. He doesn't hustle, he makes dumb plays, he strikes out too much and he shows a genuine apathy while doing it all. All he does is hurt the Mets. I can't respect a guy like that. At least Larry has the Hall of Fame waiting an awards all over his shelves at home.
I'm glad to see Pat go. Enjoy the AL! Cool move going to the team you beat in the World Series the previous season, I wonder if he wears the ring in the locker room? Probably does. Sometimes watching Met/Phils games I still expect to see Pat in the on-deck circle, waiting to hit more game changing home runs off Mets pitching.
So yea, last Phillie player I've taken the time to strongly dislike is Pat Burrell. A lot. Still.