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: Rik Mayall and Adrian Edmondson originally planned to call the series Your Bottom, so it could allow viewers to say things such as "I saw Your Bottom on TV last night."