Zubat. Nothing is और annoying than having to go through a cave where there are Zubats and आप run out of repels.
Other than Zubat, I would have to say the roaming पोकेमोन like the legendary bird trio. Having to track down the roaming पोकेमोन is so annoying. आप can't even trap them with Mean Look since they'll always find a way to escape the battle.
As for the most annoying trainer pokémon, it's definitely Whitney's Miltank.
i'd say psyduck. he waddles around with a big-a** headache, आप can't do anything about it until it gets to the point where he uses a special हटाइए for no reason!