Not necessarily because they're poorly written (the best villains require the best writing, after all) but because you've gotten so connected and absorbed in a TV show that you react strongly to characters.
Usually because they go against your protagonist/favourites (if you're anything like me

)
And don't just go for tv characters from tv shows you hate anyway... pick the ones that rile you in amongst all your TV viewing pleasure.
Off the top of my head...
- Grace, from Nurse Jackie. The antichrist of children

a passive aggressive, rebellious little c
unt. I get that she's following her mother's bad example (most recent series sees her try drugs) but she just has a very evil thing going on with her eyes.
- Pete Campbell, from Mad Men. SNIVELLING LITTLE SH
IT. Although he's got an interesting storyline going on at the moment.
- Steve, from American Dad. Worst voice in the world.
tempted to include Walter White too but... too much of a badass.