Not every pen on the desk has to be a loaner

[maywrites]

I don't think refusing to lend a fountain pen is automatically unkind. Someone who isn't used to one may press too hard or hold it at an awkward angle, and the pen is still yours to look after. I'd rather offer an ordinary ballpoint for a quick note than treat every pen I own as communal.

[morganp]

If someone just wants to see what a fountain pen feels like, I could let them try a couple of strokes on scrap paper while I keep hold of it. That's different from handing it over to use on their own.