Character mistake: Maria (Felipe's cousin) supposedly didn't understand any English (only single words like "yes") and would answer (in Spanish) "Que?" after a full sentence of English was spoken to her. However, in front of Jack, one of the girls said to Maria "Tell Jack the new English word you just learned" and Maria understandingly responded "No." There's no way that Maria could respond correctly to that question since she didn't understand any other English sentences throughout the episode.
Character mistake: Jack tells Mr. Roper (while at the Regal Beagle) that the women in the Beagle are "fantastic." Roper gives Jack a strange look (about his acting straight instead of gay, which he always thought Jack was). Jack then corrects his sentence (using gay personality and gestures). Roper is no longer the landlord of Jack's building so Jack didn't need to correct himself in front of him or care if Roper still thought he was gay.