today I found out that my department repairs eyeglasses.
So I went in to some of my national friends' office and said
"Husat i wokim aiglas?" (who works on eyeglasses?)
they asked what the problem, was, and without thinking in English I removed my glasses and said,
"I've got a screw loose."
well, I cracked myself up as soon as I heard myself say it, and took a moment to laugh.. and then realized, they had no idea of the idiom, nor why I was laughing.
"I've been accused of that for years."
I heard another ex-pat explaining the term to them as I left, absent-mindedly forgetting to interpret myself.