Politely saying NO when someone wants to borrow your pen

[Desibaba]

I have never owned a fine "Writing Instrument" but I am definitely intrigued by them. I always wonder how do you guys not lose these pens or say NO to people who want to borrow your pen for a minute. Most people innocently think a pen is only worth 25 cents when they want to borrow yours to quickly jot something down. But I wouldn't take that risk because I don't want to lose the pen or have someone damage it accidentally.