Rationalist, (and rationalism as well) is one of those somewhat rare English words---an autoantonym. A brief description of how this word is used by various people, some of whom self-describe as rationalist, will aid in understanding why this is so.
To professional philosophers, and to students of philosophy, the word "rationalist" describes a fairly specific movement in philosophy. It refers to the earliest phase of modern philosophy, and depending most heavily on the works of Rene Descartes, Gottfried Leibniz and Baruch Spinoza. Later philosophers, such as Immanuel Kant and Georg Hegel, would have fallen somewhat under the penumbra of the rationalist movement. The aim of rationalist philosophy was to describe the entire universe not in terms of either sensory data or religious revelation, but purely in terms of ideas that could be rationally apprehended and validated by the mind. Although rationalist philosophers had many disagreements on what exactly could be reached from those premises, they would all believe that things such as God, the Soul, moral law and the like did exist if they could be rationally discovered, even if they couldn't be observed directly. A rationalist, for example, would argue the question of whether a triangle with lengths of infinite size would still have 180 degrees of angle as a serious matter. They might not come to the same conclusions, but they would admit the question as a serious question. In fact, if your philosophical text contains sections about theoretical triangles, that is a good sign it was written by a rationalist.
Rationalist, as it is used in a common and in a vulgar sense, is used to refer to a belief that is called "empiricist" amongst philosophers. Although these type of self-described rationalists are usually not very articulate in explaining themselves, they usually believe in notions of "common sense", materialism and the evidence of the senses. Amongst these latter day rationalists, evidence is not only the judge of questions, but the judge of what questions can be asked. They are considered "rationalists" mostly on the basis of upholding what their culture considers uncritically to be reality.
Even if you were incorrect enough to consider Richard Dawkins or Christopher Hitchens to be rationalists, it still wouldn't clear up the fact that the word is an autoantonym: a rationalist is either a person who believes that ideas are the best way to judge reality, or a person who believed ideas are nothing but delusions. Until this autoantonym is settled, literate people will be left shaking their hands at dimestore "rationalists" like they were Henry Kissinger flashing his Nobel Peace Prize.
P.S.: This is more polemical than I planned.