This calls for a Clippy comeback. "I see you're trying to put your wedding photos into a document. Do you want me to show you how to use your e-mail client?".

I have one pair of clients who send me wireframes produced in Excel, sometimes with screenshots of LinkedIn (which serves as the inspiration for most of their ideas) pasted in. I find it quite amusing and genuinely like the clients as people, if not really as clients, so I don't have the heart to tell them how silly it is. (I did once try and get them to use Balsamiq, but it didn't end well.)

> I have one pair of clients who send me wireframes produced in Excel

There are no limits to Excel.

I've been sent floor plans in Excel where the spreadsheet has been zoomed out really really far, each square representing less than a square meter in a 20000+ square meter building.

Or banking applications where the terminal input screen (the backend is in COBOL) and batch reports are designed in (and print to) perfect square cell Excel files, one character per cell.

This goes through a very traditional corporate waterfall testing process, and everyone finds it normal.

I've had screenshots inserted into PowerPoint presentations before. That was a low point.

Sadly, I've had that a number of times too. People can be quite inventive, and painful.