This episode broadcast exactly 17 years after 'Simpsons Roasting on an Open Fire', the first episode of the series.
This episode takes place over the course of an entire year, from December 24, 2005-December 24, 2006. This is clear because of the listed dates of holidays that take place on certain days of the week listed on the calendar. In 2006, Martin Luther King Day does take place on Monday, January 16, while Columbus Day is on Monday, October 9 and the day after Thanksgiving is on Friday, November 24. This means that the episode began to take place one year before (during Season 17, which the episode Simpson Christmas Stories would have taken place) and works its way up to the present one year later.
It's possible that for the past year in the series (after Martin Luther King Day actually), Gil could have been living in the Simpsons basement this whole time, since it wasn't seen in any of those episodes. The only one of those episodes in which he appeared at all was "Jazzy and the Pussycats". This is not contradictory to which that episode takes place, since it aired before November 24 (when Gil moved away back to Scottsdale), and he could have gotten outside the house for a while.
Gil's surname is revealed to be Gunderson. This may be a reference to a character from Fargo with that surname, whose first name is Marge.
This episode has a different opening sequence. Instead of the normal, regular opening sequence, the town of Springfield has snow and everything is Christmas-themed in the opening sequence. Other episodes to have Christmas-themed openings are Season 20's The Burns and the Bees and Season 25's White Christmas Blues.
This is the last episode to air in 2006.
For the opening sequence, "Jingle Bells" can actually be heard and there is no jazz version of "Deck the Halls" in this episode while in The Burns and the Bees, "O Christmas Tree" can be heard and the jazz version of "Deck the Halls" is actually heard in there.
The title of the episode is a reference to the Kill Bill film franchise.
While the calendar is flipping through the holidays, Happy Holidays is being sung by Bing Crosby, a reference to his 1942 film, Holiday Inn.
While celebrating St. Patrick's Day, Gil is singing McNamara's Band another of Crosby's songs, in the Simpson home.
Homer asks if they can stay at a "Triple Tree Resort". This is Reference to the Doubletree brand of Hilton Hotels.
A studio album by Argentine rock musician Charly Garcia is named 'Kill Gil' as the title of this episode, though in fact is a Spanish wordplay on the title of the Kill Bill film series.
While lamenting about Marge's inability to kick Gil out at Moe's Tavern, Homer is asked by Moe if he misses UPN. By the time the episode aired, the network had been off the air.
Gil leaves a note in Lisa's lunch bag "Thanks for the bologna", despite that Lisa is a vegetarian. It could be meat-free bologna and Gil couldn't taste the difference.
The list of holidays skips July 4.
Despite the title, no one actually tries to kill Gil.
When Gil was working as Mall Santa, his skin keeps changing between yellow and light yellow.
Despite the show having Marge have an inability to say no, several times in the previous seasons, Marge has basically said no to many things, with a few examples being denying Bart beer in "Papa's Got a New Badge", refusing to let Homer stay in the house in "Secrets of a Successful Marriage", and refusing to let Homer buy a pony in "Lisa's Pony".