Luffy being stupid:
It doesn't always happen, but when it does, it's often done to hilarious effect. Moreover, as the series goes on, I think Oda gets progressively better and better at making sure it's only used to hilarious effect. 7/10
Zoro Getting Lost:
A lukewarm but highly meme-able gag. Moreover, often does double duty and becomes plot relevant. 8/10
Nami Being Greedy:
A character trait which Nami is progressively growing out of more and more. Since it's being treated like the character flaw it is, and is now mostly gone, and was realistic when it was there, I think I'd give it an outstanding 9/10
Usopp being a coward:
It is basically his whole character. Hardly even a gag. The scene in Dressrosa though, justified or not, kind of ruined it for me though. 6/10
Sanji being a Simp:
A real character ruining trait in recent times, and especially bad due to how it's treated as not necessarily a bad thing in the recent plot. At least it often ends up plot relevant and thus necessary. I had a hard time deciding between this and the true worst. 3/10
Chopper being gullible:
A character flaw that is rarely brought up, and now-a-days, never for good laughs, but was once good and at least is mostly unobtrusive. 6/10
Robin being Dark:
Always a fun panel when it comes up. Wish we saw more of it. 9/10
Franky Yelling Super:
It's kind of random, but honestly its meme-able and kind of hype. I like it quite a bit. 8/10
Brook wanting to see panties:
The worst gag. Both crude, pointless and irrelevant. Panties < Bra/Breasts anyway. Even for what it is, I feel like it could've been done better. 2/10
Jinbei:
Honestly he has no gag, and I'm fine with that.