Zubat and Golbat in most games. The annoying thing I find about them is that they're common, whilst easy to take down, yet the battle can stretch out when they are faster and use Supersonic/Confuse Ray, followed up by causing flinches by moves like Astonish and Bite. Zubat don't offer much experience points, when grinding against them early-game as well, in my opinion, which doesn't help their case.
Though I do like Zubat and Golbat as Pokemon, it's just their commonality can be a pain to put up with. :3
Boldore in Black/White.