The questions makes it appear as though you are looking for way to convince yourself or others around you not to exercise. There may be good health related reasons to avoid moderate/heavy exercise at certian points such as not physically being able to handle it, but there should not be an "excuse" not to. If you are looking for more ways to convince yourself not to exercise, you may be better off looking into some intrinsic motivation building techniques.
Sitting around brainstorming excuses not to exercise is an exercise in laziness and demonstrates a lack of commitment to your own health.
I suppose what a lot of us are getting at here is this forum/community revolves around supporting and enhancing a healthy lifestyle and your question seeks only a means to empower the exact opposite of what people are here for. Even if it was not your intent, the questions serves only to demotivate others. A much better question to pose that would be helpful to the community may be "what do you do to get yourself motivated to exercise on a day you may be struggling to get going?"