Lucas- so fickle with his women and repeats his words to all of them
Peyton- sometimes she is really needy and going after Lucas when his in a relationship
Brooke- doesn't let people in and too selfless
Haley- to quick to judge sometimes
Nathan- doesn't communicate with Haley

Lucas - doesnt think things through
peyton - doesnt evolve
brooke - gives up too easily and low self esteem
haley - this is hard. too hard on nathan some times
nathan - is taken for granted by the writers, but well i dont hate him for that but i hate it about nathan if that makes sense

lucas - ugh, in season one i just felt like he thought he was better than everyone else.
brooke - lied to everyone about her attack
peyton - didn't stay at lucas' book signing
haley - from season one to season two she changed from this normal girl to this weird 'i'm going to dress different' wife, she just changed a bit too much for me.
nathan - told haley not to come home.

so this isn't really what i hate about them, it's the things they did that i hated.... oops

Lucas - Can't just decide on his own.
Peyton - portrayed like happiness depends on other people i.e., Lucas
Brooke - selfless and insecure
Haley - easily gets upset and rushes into decisions
Nathan - doesn't spend much quality time with Haley alone