The Big Bang Theory Season 2 Episode 22
The Classified Materials Turbulence
Wolowitz has to come up with a solution when he realizes his spoace toilet is going to fail. He makes the guys pull an all nighter with him helping come up a solution using the extra parts on the space station. Basically the episode becomes a series of poop jokes and the group is unable to actually fix the problem. The best part of the episode? We actually saw Sheldon laughed! All it took was a little toilet humor.
Meanwhile, Penny is going on a second date with the guys' nerdy friend, Stuart. Both Penny and Stuart go to Leonard for advice and he tries his best to sabotage it. In the end, after Penny and Stuart ended up making out, Penny called him Leonard instead. Stuart actually reveals this to Leonard as Penny is obviously way too embarassed. There's hope for our favorite couple yet!