Stupidity: After talking to the bartender Calleigh goes back the lab and talks to Cain, he wonders if they got a false positive from the vic's blood alcohol. Calleigh then gives a detailed description of how that could happen. Cain already knows how (obviously this was done for the audience, to explain it, but in the context of the show it makes no sense).
Stupidity: Throughout the entire series the CSI's on several occasions will describe, in great detail, the procedure they are doing to another CSI. This makes no sense since they have all been CSI 's for years and should already know how it's done. Obviously this was done for the audience so they could follow along.