I believe that by and large, people tend to behave rationally. However, they aren't always honest about the reasons for their behavior. Thus, they appear crazy, dishonest, or irrational.
We see this happen all the time. For example, often when women get mad, they'll clamp up and start giving their man the silent treatment. "What's the matter, honey?" "Nothing." "No really, what's bothering you?" "I've just got a really bad headache. Now drive." Now of course something is wrong, and it's probably not a headache, but chances are you're going to have to discover on your own that she's mad that you forgot that today was her cat's birthday, and you didn't do anything to celebrate. See? Perfectly rational explanation--she just wouldn't tell you what it was.
But wait, wasn't that "reason" more emotional than rational? Maybe so. But because we're all emotional creatures to some extent, I think "rational" explanations should always account for potentially emotional responses or bases for behavior. Put differently: it's reasonable to expect people to respond emotionally to any given situation. However, this doesn't apply to clinically crazy people. Who knows what they're thinking.
