Type One: The Ignorant Idiot
The best examples of this type of creationist are people like Ray Comfort, Kirk Cameron, NephilimFree etc. These people sincerely believe that the earth is 6,000 years old, that evolution is a myth, that scientists are part of an enormous atheistic conspiracy and that they are doing god's work. The best approach with people like this in my experience is to minimize the amount of condescending ridicule in your dialogue and to try and present facts and evidence as clearly and openly as possible. Take the time to explain how scientific theories are derived and how creationism is not scientific but is actually purely religious. When they try to preach the gospel to you in the middle of a discussion about science (as Ray Comfort loves to do), don't engage them on this issue, but bring the discussion back around to science. A lot of these types of people, despite years of indoctrination will eventually see reason, don't give up on them.
Type Two: The Deceitful Demagogue
Ok, Demagogue isn't really the right word to use here, but I wanted to continue the alliteration so...
These are the people who make money by pedalling creationist nonsense (or at least try to). They may or may not believe everything they teach but either way there is a lot of doublethink and cognitive dissonance either way. Many of these people have gone to great lengths to achieve qualifications in scientific disciplines, only to then go and work for propaganda-mills like AnswersinGenesis or Creation Ministries International. They publish magazines, build