I see quite a bit of female side characters mentioned, like Rebecca or Baby 5.
I thought about it a bit, but you know what? One Piece is full of ugly ass characters. The first thought I had when I saw One Piece was not exactly 'damn this looks sick!', it was 'damn, why this artwork so ugly? What's wrong with the characters!?'
So when I consider this, I think the female side characters that play the eye candy are not even up there in the top list of waste of time. Yamato and Rebecca seem justified though. They took up a lot of time.
So far, I would say the most pointless characters would be...
1. Yamato, for being a luffy fan boy as his 'personality' on top of pretending to be a man.
2. Bartolomeo, for being a luffy fan boy as his 'personality'. He did attack Shanks though.
3. Orochi, since he kept coming back after getting killed over and over.
4. Franky and Brook. Brook is loosely tied to Roger through laboon. Tom has relations to Shanks, which makes Franky also loosely tied to the story. But overall, these two characters have no reason to exist. If they were to disappear, nothing in the story would change. Jimbei kind of ties into this as well because he has no tragic background story being told other than as a side character in Fisher Tiger's.