Oden dancing for 5 years was the most painful part to see.
On the other hand, Yamato's introduction has been the most problematic part because of the impact it will have in the series if she joins, being an absurdly tall female character with a masculine personality and delusional enough to deny her gender calling herself a man.
It's terrifying just to imagine her interations with Sanji.
I still believe she won't join, and there's certainly enough evidence that she will stay in Wano, but the possibility is still worrisome nevertheless.