Scanning, I sort of agree with the majority of posts here re: about keeping it in perspective. However, I can also see you're a sensitive person and why you're morally aggrieved - it's only a little thing, but it rankles. And ali's right - if fat boy becomes a serial offender, there could be a (cumulative) explosion on your part. So it might be best to forget it for now. Mind you, if I were you, I'd tell your mate from the other department what happened, and just contrive to talk about the biscuits "in passing"/ "as an aside" in front of the individual in question...just to make a non-specific point...