The One After the Superbowl, part 2 - S2-E13
Visible crew/equipment: When Joey walks into the bathroom and starts whistling, the shadows of the camera and a passing crew member can be seen on the door of Chandler's cubicle, then the camera's shadow moves as Joey walks toward Chandler and also when Joey's about to stand on the toilet.
Answer: The statements that she's contradicting (that it is common, it happens to every guy, and it's not a big deal), are the things that a woman commonly says to a man who is suffering from erectile difficulty, typically to assuage his bruised ego. However, most men do not believe that these statements are true, as evidenced by Chandler's outburst. He's so caught up in the proof that women are lying about it that he gives himself away.
Rooster of Doom