Hearing about Regular Show replacing a broadcast of How the Grinch Stole Christmas reminds me of the time in May 2002 when a broadcast of Greg the Bunny was replaced with an airing of The Bernie Mac Show (and it stayed that way for the rest of the month.... Greg the Bunny was soon dropped while Bernie Mac remained for a few years). I was never that interested in The Bernie Mac Show in the first place (though I did watch it at times), but after that I've really hated the show and Bernie Mac (though I guess it wasn't his fault that his show was scheduled in place of one of my favorite shows at the time).
But then again, this is different. I was expecting to see Greg the Bunny, a new show at the time, and The Bernie Mac Show was on instead without any announcement. How the Grinch Stole Christmas is a one-time special which has been broadcast every year and gets rebroadcast multiple times each Christmas season, on multiple channels (I am suprised that it now airs on ABC Family and ABC, for awhile I was wondering if it still aired on Cartoon Network but judging from this thread it obviously does), and Regular Show is a show that I really like. I'm not going to hate Regular Show because of it.