To think rationally means taking the appropriate action given one’s goals and beliefs — what we call instrumental rationality — and holding beliefs that are in synch with available evidence, or epistemic rationality.
Again, the competing definitions of what it means to be rational make this difficult. Instrumental rationality takes the goals and beliefs as givens, and simply seeks the most efficient way of connecting them. A murderer or drug addict could exhibit rationality within those parameters. Epistemic rationality involves more of a value judgment on those goals and beliefs, but as anyone who has ever attempted to argue a friend or relative out of some crazy opinion knows, even available evidence can be undermined by mistrust of the source, or the suspicion/hope that later evidence will contradict what's now being asserted as fact. Ah, well, I was already pessimistic about human nature anyway.
This seemed kind of interesting:
I coined the term dysrationalia — an analogue of the word dyslexia — in the early-1990’s in order to draw attention to what is missing in IQ tests. I define dysrationalia as the inability to think and behave rationally despite having adequate intelligence. Many people display the systematic inability to think or behave rationally despite the fact that they have more than adequate IQs.