We used to have this problem with me and my friends too. We called it "BIC-ing" the lighter, for some odd reason. A stoner moment I guess.

But yes, it does get annoying. Especially when smoking. You light a joint or whatever, you're good and high and end up forgetting about your lighter. You go home, smoke a bowl only to find out that yous aw your buddy snag it. It was all by accident mind you, but I know when I'm putting something in my own pocket, I know what I'm doing, so maybe it isn't on purpose.

Anyways, the best thing to do is just to get the lighter back right after they're done using it. They light their smoke, great, now ask for your lighter back before it goes missing. It isn't rude, but it saves you $2 and a trip to the store to get another one.

So just keep an eye on your lighter.