Put sensitive files on removable card. When lending, remove said card. Problem fixed. This does leave traces like file names remaining in 'file history' list, but this is not very dangerous without the actual files, and if you have enough brains not to name them "me&she69.jpg" or "confidential_customer_data.doc".
The problem, of course, would be that the files are not in /home/... . Maybe some clever sym-links could solve this. On my fedora box, i have /home on one partition, and several /home/xxxxxxx folders on other partitions, and it works well. Also, the ability to save on card by default for some apps (like camera) might be important
Here's how the system might work. Let's say you have several calendars under /home/calendars, and some of them are private. Have a script that moves calendars considered as private to the card and sym-links them back in /home/calendars. Apps looking there would see no difference, but the files are gone when you remove the card