Last night, after Larry Moran‘s interesting and informative talk, a student (not one who had taken my evolution course, I should say) brought up irreducible complexity. Not flagella, as I was expecting, but the bombardier beetle. How could this evolve when you need all the chemicals and they explode when you combine them? You know the story. Larry responded graciously (note: that is not a typo) and explained about shifts in function and used an example from his own area of study, biochemistry.
For those who think that the bombardier beetle is a problem to explain, here are some resources you may find helpful.
Bombardier beetles and the argument from design (Talk.Origins)