Yeah, I've definitely experienced irritability before. I can't pin it to anything in particular though. Some days if I have to extend my fast longer than I'd like I can become irritable. Having something to work on or distract me helps with that though. Also I think going too low on calories for too long.
Oh, and I really think that dehydration can make me more irritable. If I remember correctly, dehydration can cause a rise in hormones that make you more aggressive. This would make sense if you had to fight others for access to scarce water supplies. Anyway, I may be totally off-base with all my theories, but I can sympathize.