Ichimaru Gin - Bleach
Such a waste… All that time spent wondering how awesome Gin would be (should be) down the drain as cannon fodder. Ridiculous.
Takayanagi Masataka - Tenjou Tenge
The single coolest character in the series, I enjoyed watching him kick the main character's ass at the beginning.
Most of the characters of Hunter X Hunter
Wow did Greed Island screw up a good thing. Yeah I know the recent chapters before the great hiatus have been good. Hiatuses have really killed interest for me, and ditching awesome characters like Kurapica for Greed Island was cold. Remember when Hisoka was awesome? What happened?
Teresa - Claymore
At one point I thought the plot of this manga was actually going somewhere. I was and am sadly mistaken.
Dark Schneider - Bastard!
The series itself is great, but it's half finished due to a lazy and/or sick mangaka, so the story has been half finished for a LONG time. Seriously, ongoing since 1988 and only 26 volumes.
Vegeta - DBZ
If only planet Namek had never existed and the series had just ended after the Saiyan saga. But alas, Captain Ginyu and Frieza, and more did come into existence turning Dragon Ball into the soul sucking, endless abomination it is today!