One (or more) of the characters has a particularly foul mouth, so another character decides to institute The Swear Jar
so that they have to pay up every time they use rude language. Hilarity Ensues
as the character who used to swear like a sailor either drops an unfathomable amount of cash into the jar or ends up having to self-censor everything they say. Also expect the character who instigated the jar to end up falling foul of their own rules and having to put money in as well. May also appear as a more generic Forfeit Jar if any character is particularly prone to specific words, phrases or acts.
Don't expect it to last beyond an episode.
- There's a Canadian Tire commercial where, because of botched attempts at home repair due to not having the right tools, a man's swear jar ends up paying for the tool being advertised.
- There was one Budweiser commercial involving the profanity jar, with proceeds going to the next case of beer -- profanity ensues. 
Live Action TV
- Shows up in Hot Fuzz: Nicolas and Andy have other characters dropping coins in he jar for them as they have a heated argument, and both turn aside to politely thank them for paying in.
- The Richard Pryor movie Moving had one. It is shown used normally to punish his daughter for swearing. She then pays in advance at one point so she can cuss him out. Later, when the "move" goes very badly we see Pryor prepare to let loose... instead the movie cuts to the jar totally stuffed with cash.
- Legally enforced in Demolition Man.
[AC: Web Original]]
- The Salvation War has a variation on this; any time one of the researchers looking for a gateway to Heaven wishes aloud for Einstein/Feynman/insert-Nobel-Prize-winner-here to magically appear and help them solve a particular problem, they cough up a couple of bucks. Last Friday of the month, everyone goes out drinking with the cash.
- The Simpsons finds Homer having to deal with one of these whilst he's building a doghouse for Santa's Little Helper. He ends up shouting things like "Fiddle-dee-dee!" after stepping on rusty nails, and puts enough money in the jar to enable the purchase of a rather large and cosy doghouse -- which is good, since the one Homer built sucked.
- American Dad! - In fact the family has dozens of jars, one for each word. Including "moist".
- Director Robert Rodriguez didn't want the crew swearing in front of the young cast in Spy Kids, so he instituted one of these. One of the crewmen slipped up, and went "Oh shit...ake mushrooms", in order to avoid the fine. Rodriguez liked this so much he included the line in the move.
- During the shoot of 2005's Chronicles of Narnia: The Lion, the Witch, and the Wardrobe movie, according to the commentary, only Georgie Henley (playing Lucy) was doing the collecting herself.
I'm sure there's more.