Bottom's Up - S1-E5
Continuity mistake: When Richie and Eddie are on the roof and Richie starts his rain dance, watch the bottom of his trousers. To start of with he pulls the hem up to around his shins. He then starts and pulls his groin or something and stops and at this point the right hand trouser falls back down his leg. Then straight afterwards in the long shot you can see that it's back up again without him pulling it up.
Trivia: Perhaps an odd bit of Trivia, but Dr. O'Grady's treatment ("have your personal organ enhanced so that it comparable in size to a fully grown mountain gorilla") is not as big a ripoff as it sounds. A fully grown gorilla has an erect penis length of around 1.5 inches (on average).