Mt. Coronet is horrible when you're trying to go through the upper floors because of all the Golbat and Bronzong. They're both so freaking common... and both so freaking annoying to kill. Repels don't always work, either. That entire dungeon is just annoying to get through because of their high spawn rates.
Abra isn't annoying unless you're trying to catch it, and if you have a Gastly with Mean Look (in Johto), a Pokemon that can instantly put it to sleep, or something, then it's easy.
Tentacool can be annoying for sure, though Basculin is probably even worse in terms of how many you see. Tentacool, though, can poison your team, and that leads to problems.