I often eat lunch in my cubicle, reading or surfing the internet. Since it's a cubicle and therefore I have no door, people often stop by with a work-related issue. Generally if I mention I'm at lunch, they go elsewhere for their answer, no big deal.
Here's what bugs me (and happened yet again today).
A coworker who KNOWS I am on lunch asks me for help on a regular basis. She starts with, "I know you're on lunch, but..." and her questions are not generally short ones. It's especially aggravating because she normally takes longer than allowed for her lunch break.
Some day I hope I have the guts to just tell her, no, I am on lunch. Please go ask someone else. This is my personal time, even if I happen to be at my desk.