Mine is undoubtedly: Chris! He was such a selfish, annoying jerk! I'm running out of negative adjectives to qualify him. Not only because of the way he screwed everything up between Luke and Lorelai but also for how he was careless regarding Lorelai and Rory. He was never there but the few times he was he wanted to control everything and ratted out (about Rory moving in with Logan for example while she made it clear she wanted to tell her mom herself). Plus, I just can't stand how he keeps saying "Lor" and "kiddo".
April was alright. I mean she didn't cause the breakup, Luke did by keeping Lorelai out. I can find her anoying when she tries to set up Luke with her teachers as if Lorelai had never existed and the engagement hadn't been broken off in such a tragic way.
Kirk is adorable IMO.
I find Lane sometimes annoying.
The first time I watched the show I just couldn't stand Jess and Logan but after the third time they're okay. Dean on the contrary really gets on my nerves now!
But on the whole I just loved everyone, some of them annoying me at some points like Rory for example (Luke and Lorelai are the only ones who never annoy me, I could disagree with some of their actions but I couldn't not like them) and one that I profundly disliked all the time: Christopher.