Lol, luke trying to negociate only for the GM to tell him that won't do is a the funniest part.

I mean, he might be right?

I can't recall if Devil fruit's weakness activates with all water, or sea water specifically, but if it's sea water specifically, then Acid doesn't count.

Except this is a whale who lives in the ocean, so surely a lot of seawater would end up in their stomach as well...

I took a look at the wiki and apparently it's all water but it doesn't apply if the water is flowing (Like if you're taking a shower or it's raining).

I always thought it went like they're weak to salt water in general but they can't swim in any water at all.

As far as I'm aware, you can't swim at all, but if seawater touches you, then your power is nullified and you lose all your energy.

Luffy couldn't even swim in Skypeia but him and Robin were able to use their powers through the could water to save Usopp.

Well, I don’t know about Robin, but Luffy’s DF makes him rubber. While he can’t USE it in water, his body is still rubber, so using it out of water means it will keep going through water, and he can still be stretched by outside forces in water. It’s how he didn’t drown back at Arlong Park, the group pulled his head above water while he had his feet stuck in concrete.

Specifically it’s seawater that drains his strength. Paramecia are still affected by their devil fruit, since it’s a physical transformation on a fundamental level, but they basically become helpless and can do anything while in contact with seawater. So Luffy in arlong park was able to have his head stretched above water by someone else, but he couldn’t generate the force to move his arms or “throw” his head above water.

Devil fruit users have two separate weaknesses. Being submerged in water (not merely touching, but also not just salt water but any reasonably water-like liquid) saps all of their strength, and touching the material called Sea Prism Stone suppresses their devil fruit abilities.