Didn't happen to me. But I remember a coworker of mine getting fired because he put laxatives in his own lunch bag. Some d******d kept stealing parts of our lunches. Turned out, it was our supervisor.
Edit: Jesus Christ...that's a lot of upvotes
Edit 2: I'm not to keen on the specifics since that coworker and I weren't exactly friends or anything. Just kind of had simple conversations during lunch and whatnot. Apparently it is illegal to poison food with malicious intent. And some of my friends who worked there said he got into some legal trouble because of it. Nothing came of it from what I heard. But that's about all I know.