I don't know how people who do that stuff can live with themselves. I can't even live with myself when my co-worker gives me rides to work (just had surgery) and refuses to take any gas money.
Just this week at work we had our monthly birthday cake and we keep it on a vacant desk that is just off the common walkway. At 9:00 in the morning the cake was half gone because random people just kept helping themselves. Man the cojones on those people!
The worst thing in my experience was at a former job. Our office was 24/7. We had new-hire classes going on in the basement for a shift that was like 4p-12a. The basement wasn't heavily trafficked during those hours. The instructor fell in the hallway while going to make copies. She had a concussion, and couldn't stand up, and left bloody handprints on the floors and walls as she tried to get herself up...None of the 20-something kids ever snuck out to get a pop or anything. So...about a month or so later she returned to work. I had subbed for her class while she was out. For her return, we planned a huge potluck/party for her. Some @$%&$!#^!@ STOLE her 6 foot party sub. How in the world do you do that???!!!! I really hope (like PP said) that REALLY bad Karma came back on that person. It was just EVIL. The next day, I made up my famous crab puffs and chicken fried rice for the whole group, not knowing they'd already ordered pizza

I like my current company's take on lunch thefts. It's theft, plain and simple. If you are caught/proven to steal, you will be terminated.
Sorry for the long post...