blown over with a feather?
a monkey's uncle?
We just got a phone call from a contrite alumni of the school. This gentleman was clearly atoning for his ill-spent youth and wanted to return - 10 years too late - books he'd borrowed while here. After putting him on hold and cracking up, I pulled it together enough to inform him that we were very grateful for the gesture, but it really wasn't necessary that he pack and ship them to us.
A cash donation would do just fine. (Of course I didn't say that, but I wanted to!)