Ok, first of all, the reason I didn't delete the entire sentence is because his retardation is a recurring gag.  Second, gay jokes are also recurring gags because they appear numerous times throughout the series.  I have no problem with creationists getting slammed as I'm not even one myself (more like creationary-evolutionist), so don't play the "you're just offended" bullshit because it's just that: Bullshit.  Also, the throwaway gag thing does hold water because they could have had the entire episode without it.  The episode would have held just as much merit and made just as much sense without that gag.  Tell me, how is the creationist gag essential to the plot of this or any Family Guy episode?