Deliberate mistake: In this episode, Ray tells Amy's mother that Debra no longer reads his column, although she did when they were dating "and she was wooing me." But in an earlier episode, Ray proposed to Debra in his very first column - so when they were dating, he didn't have a column.
The High Life / Best Friends - S2-E10
Deliberate mistake: In "The High Life", there is a scene where Stinky submerges his head in a tank of water. He delivers the line, "Gee willickers, it's still ticking", and everyone somehow understands what he is saying with his head underwater.