Here are my top 5:
5. Ash not evolving his Cyndaquil. I mean, after seeing the episode "You're a Star, Larvitar", I thought for sure he was going to evolve it. He loses to a guy who goes on about the importance of evolving your Pokemon. Then, he sees this guy training his Quilava, and realizes that it's Cyndaquil's evolved form. He then remembers what the other trainer told him about the importance of evolving your Pokemon in order to prevail in the Silver Conference. He was just begging to evolve Cyndaquil there, but... typical Ash...
4. Brock not getting Charmander in the first season. He deserved it much more than Ash did, but, of course, Ash just had to have all three starter Pokemon.
3. There are never any Nintendo Events in Canada, like a previous poster stated.
2. In my opinion, the Pokemon Heroes dub was terrible compared to the Japanese version. They cut out the beginning, the voice actors were just plain bad in general (I have no idea why they had to give Latias and Latios those awful screechy voices), and we had to listen to rehashed Pokemon theme songs instead of the catchy songs they had in the opening and credits of the Japanese version.
1. The fact that Ash never seems to win any tournaments. The Orange League was an exception, but every other time, it seems he's booted out in the quarterfinals or before, only for us to see the person who beat him get beaten by another trainer.