Used in informal situations, often to express disagreement or skepticism about someone's opinion. I think he's the best player on the team, but my brother says I'm all wet.
Pro Tip 2/3
Figurative Meaning
Doesn't relate to actual water. It means someone's beliefs or statements are incorrect or unfounded. If you think that's the correct answer, you're all wet.
Pro Tip 3/3
Conversational Tone
Often used among friends or peers. Might be impolite if used with someone you're not familiar with. During the debate, he told his opponent that her facts were all wet.