:smack:
Please elaborate. I thought the first episode was where Aunt Bee comes, and Opie doesn’t like her, and she almost leaves. I also know of the Danny Thomas episode that introduced Andy and his son Opie. Don’t remember any called-off weddings early in the series (I remember one kinda called-off wedding when the Darlings discover it’s Barney Fife and not _____ (can’t remember) in the wedding dress, and another where a couple of con artists try to get money out of Barney for breaking an ‘engagement.’).
This happens in Cinderella III: A Twist in Time, a direct to DVD Disney cartoon. Anastasia, one of the stepsisters, has been magically disguised to look like Cinderella, while the real one’s been kidnapped. Cinderella rescues herself and gets back to the wedding of her stepsister and the prince, just in time to hear Anastasia say, “I…don’t.” She’s taken a level in goodness. She changes her appearance back to her real one. Cinderella and the prince are married by the minister.
A variation happens in A Different World. Whitley’s getting married to some guy, who’s said the “I do” part, and just before Whitley does the same, Dwayne bursts into the ceremony, and asks if she’ll marry him instead. She says, “I do”, while looking at him, not her fiance. The minister asks which man she considers herself married to. I think that was the end of the episode. I don’t know what happened after that.
Does Kill Bill count?
Neither the bride nor the groom called it off, but somebody certainly objected, so sure.
The Princess Bride’s wedding was mostly uninterrupted, but was technically invalid since they had skipped the “I do” part, and Buttercup was rescued before that minor oversight could be rectified.
The wedding in Beetlejuice was interrupted by Alec Baldwin riding a giant sand worm.
It is more common than not in soap operas. Alison Sweeney’s character on Days of Our Lives was 5 for 13 (5 completed weddings, and an additional 8 that were interrupted) before her most recent wedding, which was completed, only to have the groom arrested at the reception.
Only the Lonely (John Candy/Ally Sheedy/Maureen O’Hara movie)
*Sanford & Son *(I think the pilot episode)
No weddings have been cancelled on Game of Thrones but a couple of receptions got a little wild.
That was the wedding rehearsal so not quite.
The Princess Bride. The wedding doesn’t finish technically because of the fun being had storming the castle.
At risk of my man card - in “Princess Diaries 2”, the princess calls off her wedding, but the queen ends up marrying her factotum or some-such. No license mentioned, but then again, she is the queen.
“Foolin’ Around” with Gary Busey… He crashes the wedding by flying a hang glider through a church window.
There were a couple on The Simpsons (not including the “future” one); Principal Skinner and Mrs. Krabappel, and Otto and some one-shot character. Also, there was a wedding ceremony with Mrs. Krabappel and Comic Book Guy that was interrupted, although I don’t think it was a real wedding.
Also, I don’t know if this counts as “once the service has started”, but Julie’s wedding in Australia on The Love Boat; the groom was a no-show (it turned out that he had an incurable disease and didn’t want to put Julie through watching him suffer through it).
IIRC, Dwayne runs to the alter, the minister says, “I now pronounce you man and wife”, and Dwayne calls Whitley’s mother “Mom.” They even show Whitley turning away from her fiance and towards Dwayne in the opening credits of each episode of the next (and final) season
Not the pilot, which I remember involving an auction for a porcelain figure of some sort, but I think the second episode; when asked, “Do you…”, Lamont’s fiance says “No”, then the minister continues on as if she had said “I Do” before she makes it clear that she doesn’t want to marry Lamont.
The movie In and Out has both the called off wedding and the “as long as we’re here” subplot (though only for a renewal, not a full wedding, on the latter).
Pam and Jim’s wedding in “The Office” had this as a possible subplot, but we discovered later that they got married before their wedding in a ceremony of possibly dubious legality.
The most surprising thing about the episode was how quickly Pam and Jim were able to straighten out their hair and re-do their clothes after being drenched with spray from Niagara Falls. 
I Love You Alice B. Toklas (Peter Sellers film)
Will & Grace (at least two- one for Will and one for Karen)
Northern Exposure
In the ST: The Old Stuff episode “Balance of Terror,” Kirk is officiating over a wedding between two crew members when the ceremony is interrupted by a Romulan attack.
Home Improvement’s Al Borland and his girlfriend of three years, Dr. Ilene Markham, decided at the wedding that they really didn’t want to marry each other.
That’s the episode. It starts with Rose, getting married. Rose was Andy and Opie’s housekeeper. When she married and moved off, that was what caused the need for Aunt Bee
The TV series Friends begins with Rachel showing up at the coffee house after having just run out on her wedding.
The other princess is crying so hard he takes pity on her and lets her run off to her troo wuv. He and Cinderella work things out later.