Joffrey Baratheon. Ramsay Bolton. Olly.
These are some of the most evil, despicable characters inhabiting Westeros, rightfully despised for their actions, and are the worst characters on the show in that sense.
But what about the characters who don't necessarily do bad things, but are just bad characters?
Two of Game of Thrones biggest strengths are its cast and characters; they usually get the right actor for the part, and even the minor players fit the world and contribute to the story.
Occasionally, though, they do get it really wrong. This isn't focused on the many random smaller characters who didn't really contribute much (like, say, Mero), but those with at least a decent role in proceedings, who were underwritten, badly acted, really irritating, or just plain boring.
Thankfully everyone in Westeros gets their comeuppance eventually (and many of these already have), but whether they're long dead, still living, or a combination of the two, they represent the worst the show has to offer.
Kevan Lannister is ostensibly a key supporting player around King's Landing, featuring prominently on brother Tywin's war council, and later the Small Council, even being named Hand of the King.
But despite his apparently glowing achievements, Kevan doesn't really do anything, or have any character at all. He's just kind of there, and more often than not treated as a bit of a bumbling idiot (so is Mace Tyrell, but at least that's the way he's supposed to be and it's played for real laughs).
He's not particularly interesting, and doesn't get the chance to really operate politically, even after Tywin's death, but merely stands around as a somewhat familiar face.
In the books he is similarly in the shadow of Tywin, but mostly because he recognises his brother's tactical genius and agrees with his decisions. He's a much shrewder operator, has a bigger part to play in things (in particular in working against Cersei), and is killed off (I won't say by whom here) because he threatens to bring order to King's Landing.