I was always wondering, is it possible to deliberately chose to be irrational ?

Great question. There seem to be cases when a person might rationally chose to act irrationally --as occurs in Shakespeare's play Hamlet when the main character, Hamlet, acts as though he is mad to confuse his father-in-law (and, it turns out, the murderer of Hamlet's father) and this buys Hamlet more time in his contemplating how to avenge his father's death. I believe that USA President Nixon --and I am sure some other world leaders- sought to project to potential enemy states that he was capable of being irrational. There also seem to be cases of when persons deliberately put themselves into states of mind in which rationality goes out the window, as when a person deliberately becomes heavily intoxicated or allows their passions to be so completely unedited that they are in an 'anything goes' mode.

Apart from such cases, there may be a different, more paradoxical case, and perhaps the following is what you have in mind. Imagine a person is deliberating about whether to choose A or B and the person knows that choosing A would be highly irrational (e.g. there are very good reasons that the person knows that choosing A would be 99% certain of being profoundly undesirable and there are very good reasons or she is 99% sure that choosing B would be desirable). Under those circumstances, is it possible for the person to choose A? I think it is if we are using a somewhat narrow understanding of what is rational and irrational. Some philosophers have distinguished between rationality and feelings or intuition or faith. Pascal, for example, once claimed (rough paraphrase) that the heart has reasons that the mind does not understand. Such a remark suggests that one might think of 'rationality' as a primarily intellectual judgment rather than "following one's gut feeling" or something like that. Given such a demarcation between reason on the one hand and gut feelings on the other, I think we can imagine a person deliberately acting in ways that (from an intellectual point of view) are irrational because (from the supposedly "gut level") they have other grounds for their decision.

This juxtaposition between reason and gut feelings actually came out in a USA presidential election. The Goldwater campaign had a slogan: "In your heart, you know he is right." Goldwater's opponents came up with this reply: "But in your guts, you know he's nuts"!

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