(a) three facts about them from my personal canon/fanon
(Lucius, Hitsugaya, Ginny, Draco, Blaise, Switch, Trinity, Dudley, Gollum, Hibari)
(b) a reason he/she sucks
Urahara Kisuke (Bleach)
So, I love Urahara, but I will never be okay with him using Rukia to hide the Hōgyoku. He wasn't just risking her life; he was going to turn her into a human without her knowledge or consent. Not cool, Urahara. Not cool. :|
I can't stand that she basically turned into Nynaeve as the series progressed. Talk about history repeating itself.
Molly Weasley (HP)
She sucks because she's overbearing and meddles in things that are not her business. Like killing Bellatrix. Even Bianchi from KHR would have been better in that role, because at least she's got the Poison Cooking skill (why do I want to write that scene now... "POISON COOKING ALL YOU CAN EAT BUFFET! GYAAAAH!"... though I think Bianchi might actually sympathise with Bellatrix >.>). Molly's demonstrated zero combat ability in the series, and while I get that it's a ~*~Significantly Symbolic Character Moment~*~, it's an annoyingly obvious one. No, JKR, being a mother does not necessarily make you a badass mother.
Remus Lupin (HP)
He ruined Harry's first-ever birthday party with his doom-and-gloom prophesying. 'Nuff said.
Aizen Sōsuke (Bleach)
Aside from his less-than-pleasant personal qualities (which I actually think make him a great character), Aizen sucks because he lacks a "why". Sure, he wants to be
Lindsay Peterson (QaF)
The way she behaved re: her affair in Season 4 annoyed me, because she was ever the martyr when Mel had a one-night stand with what'sherface in Season 1.
Bovino Lambo (KHR)
HE IS ALWAYS STEALING EVERYBODY'S FOOD WHAT A WANKER. Adult Lambo is different, but he sort of freaks me out. >.>
Roland Deschain (DT)
The way I read the series, Roland needed Eddie, Susannah, and Jake to dislodge him from his hopeless circular path. He sucks because he doesn't learn on his own and, if given a chance, repeats the same mistakes.
I don't consider movie!Denethor to be Denethor -- it was great dramatic acting, but in canon, the Steward of Gondor was too strong to fall prey to the palantír. He sucks for sending Gondor's forces to Osgiliath, however, because he knew the enemy's might. If he wanted so badly to make a stand, he should have led the charge himself.
Just these few today, for I had to do actual work at work today (amazing!) Tomorrow: why Grimmjow, Boromir, Arya, Legolas, Jaime Lannister, Daenerys, Jon Snow, Debbie Novotny, and Eowyn are awesomecakes. :D