Sometimes I wonder how certain English expressions translate in Japanese and will look them up on ALC. The other day I came across an interesting one.
I was wondering what the most natural way to express "you know me better than that" would be. One of the listed translations caught my eye. 「水臭いなぁ」
Eh? Something about stinking of water? I did a little Googling and found an explanation. It's actually used more to mean that someone is being too formal or stiff. According to this website, the expression is said to have originated in Osaka. The reasoning is that cheap or unappetizing soup wouldn't have much flavor...it would be light and watery. In preparing soup for someone, like a friend or guest, only a cold-hearted bastard would intentionally make soup like that. Thus "it tastes watery" or "it smells like water" came to mean that someone was being cold or unfriendly.
The more you know.