Plot hole: The apartment block where Will lives supposedly has the same layout for each floor of the building. Yet in "Yours, Mine or Ours" the room 12D is seen as located right in front of the elevator, the same location as Will's apartment door - however Will's apartment is always seen as 9C.
Plot hole: In "Alley Cats" when they are bowling and Grace is losing, she says she's fine with it and she knows how it feels to be her middle sister, then Will reminds her that she's actually, "The baby of the family looking for Daddy's approval." However, in all later episodes, Grace is portrayed as the miidle child with a younger sister, Joyce and an older one called Janice. This mistake is made in a few other places through the show, where Grace either refers to how old she is (youngest, middle child etc) incorrectly.
Plot hole: In the bowling alley scene, Ellen states that Grace would need to knock down 27 pins in order to tie. Will and Grace then have a conversation, and Grace gets a strike with her next ball. They then start gloating that they have beaten Rob and Ellen, but the scores don't add up, and they couldn't go into the lead on that round.
Plot hole: Will and Jack are out on the patio talking about the first time they met at a party (implying in college) and how Jack convinced Will to come out, but in S1E6 Jack talks about Will's favorite book in elementary school. I am re-watching the show now, and I am sure they have a conversation about hanging out as kids. Makes no sense. Time 1 is season 1 and time 2 is for Season 2. (00:06:33 - 00:13:10)
Plot hole: In this episode during the flashback scenes, it is shown to us that Will comes out of the closet during his freshmen year of college during Thanksgiving Break, when they spend the weekend at Grace's Parents house. However in the season 1 episode "William, Tell" Grace claims that Will came out to her at senior year of college during Christmas Break. Quite a difference for such a memorable time.
Plot hole: Jack spends part of this episode clumsily teaching Karen basic steps of the fox trot for her wedding dance with Finster. However, in season 4, episode 16 ("A Chorus Lie") It is established that Karen and her husband Stan have, for years, performed an annual spotlight dance at their Valentine's party on Shelter Island. Later, she and Will are seen beginning a rather elegant fox trot to "Someone to Watch Over Me," complete with spins and a dip.