It's very irritating. The same people always ask me to borrow a pencil or pen, but they never give it back. When I started to ask to get it back, they started to go over and stand by the door, or go to their friends to talk, so that I don't have the opportunity to ask them for it. Sometimes they said that they had lost the pencil, but a few days later, they brought it back to class to use it, right in front of me. It's the same with paper and other supplies- I'm not a walking, talking, free store, for pity's sake.
I like stationery, so I sometimes buy nice mechanical pencils for myself (not that often, but I have about 3 or 4 right now). I've lost many of them because I lent them to others. Pencils are one of the few things that I buy slightly expensive versions of (sub $10, but still a decent amount for a pencil), and I hate that people steal them. I'm just going to keep some cheap pencils with me in case someone wants to borrow them, so I'm not paying for their irresponsibility. Does this bother you if someone does it? Do you give things back if you borrow them from someone else?
Yes, I know some people can't afford supplies. I'd give supplies to someone if they actually could not afford to buy them. However, the people who mooched supplies off of me were well off, and could afford dozens of new clothes, iPhones, iPods, etc. But not a $2 pack of pencils.