Great question!
I am in the Jaminet, Kresser, Harris camp when it comes to starches. So I don't view starchy veggies and tubers as cheats. So potato and rice are part of my daily diet. I also feel if you can tolerate diary it is not a cheat, as long as you are getting it from a good source (grass fed, local, raw). Also I think having a bit of alcohol or dark chocolate is not cheating either. Just should not make a good portion of your diet. It's part of living a social, healthy, and balanced life. Not everything that tastes good or not necessarily the best for you has to be looked at as bad or evil. Let's not be puritans here.
Examples of cheating/20 cheating (the 20 part) for me is going out to restaurant restaurants and eating CAFO meat, foods cooked in rancid veggie oils, having ice cream (which I do try to get from local farms with minimal ingredients), and once having beer once in awhile while out (gluten). beer/alcohol. I also think baked paleo foods can also fall into this category. They are not real food IMHO, but I have see no problem having one indulging yourself once in awhile. Another cheat I would also consider is protein shakes a cheat.
