Red vs. Blue would normally not qualify for this, since cursing has almost always been one of the trademarks of the series. However, the last half of season 1 and the first half of season 2 were almost completely clean (Rooster Teeth had been trying to make the series more kid-and-work-safe). When the creators decided to reintroduce profanity into the dialogue, they did it with Caboose's "mental image" of Church, who spouted off more over-the-top vulgarity than had ever been heard on the show up to that point, a pretty major wake-up call to the audience.
"The fuck's a condom?!" Notable because this is the first time 'fuck' is uncensored and uninterrupted.
kurtjmac barely ever swears, preferring "crap" and "nuts to you" and occasionally dropping a "hell" or a "damn". In the most recent episode of the Mindcrack Ultra Hardcore series (in which well-known MinecraftLet's Players duke it out last-man-standing-style while running a difficulty-increasing mod), he goes from full health (and a very complete player-killing kit to boot) to dead, in less than a second, by glitching into a block because his (four) dogs teleported to him while his boat was near land, in memory-intensive terrain, on a laggy and crowded server. His response? "Motherfuck-" *cut to old-timey We Are Experiencing Technical Difficulties slide*
The earlier episodes of lonelygirl15 were like this. Bree swears precisely once in the entire series, in "I Probably Shouldn't Post This...", when she is defending the Hymn of One in a heated argument with Daniel: "It's my beliefs! There's a million fucking different religions in the world!"
Notably, Linkara (who never uses stronger language) actually referred to a character as a twat in his JLA: Act of God review. Also in that review, he uses the word "goddamn," which is all the more appropriate as the comic was partly written as Christian propaganda.
In one crossover review with Bennett The Sage, he had Bennett do the Precision F Strikes for him. Linkara paused when most people would curse, and Bennet said the F-word for him.
And then when he made an appearance in Bennett the Sage's Masterpiece Fanfic Theatre in which he was tied to a chair and forced to listen to his own teenage fanfiction, he WOULD have dropped an f-bomb...if Bennett hadn't conveniently gagged him.
Although, he does say "Son of a bitch!" (his strongest swear, aside from a bad imitation of him by The Nostalgia Critic, who made him say the F word in a faked apology video) when he reaches his breaking point, much to Bennet's amazement.
Cry for Justice had him as close to dropping the f-bomb as he'll probably will ever get: "This is a freakin' joke!!!"
Used spectacularly in Survival of the Fittest. Yes, while most characters swear like sailors, cute, meganekko, sugary sweet Louise "Lulu" Altaire manages to pull this off. When she meets Lenny for the third time, after he has just killed her friends the previous times, this time she's prepared. She's killed people, she has a gun and isn't afraid to use it.
Lulu: See this thing, Lenny? Now you take your fucking hands off your handgun or I'll blow a hole through your head.
(Rage builds up within the Nerd) F...F... Curse! Curse, Goddamn it! Mnh! I used up all my fuck points during the last 107 episodes. I don't have anything new. I gotta rely on the old tricks. (Begins to fight the game cartraige RPG-style) All right. Let's try the ClusterFBombs. Fuck this fucking piece of shit fucking shit fucker game! (Game attacks the Nerd) UGH! Uhh, gotta go for the Precision F-Strike. Oh, how this game lures you in with its appealing gameplay, and charming atmosphere, and then bends you over and FUCKS you to Hell!!
Brad Jones in Rock Its Your Decision. He was perfectly willing to let the worst stereotype Christian ever rail against Rock Music (which he quite likes apparently) and he would just laugh. Then he brought up lifestyles of these people. (The following is in Bluevision.) Hinthint, heusedthewordhomosexual.
"I'll say this once Laurence, I hope it's understood./Get back in your van, and get the fuck out of my neighborhood".
Chuck Norris vs. Abraham Lincoln: "I AM CHUCK FUCKING NORRIS!"
Hitler vs. Darth Vader: "Now stand at attention, and Sieg fucking Heil!"
Extra Credits has gotten worked up over subjects before, but has always kept it's language clean. But Call of Juarez: The Cartel's completely backwards depiction of human trafficking finally warranted a "That is f*bleep*ing disgraceful".
This guy answering a prior video's question as to why God won't answer prayers.
"Seriously? I know this is innappropriate, but what the fuck."
Interestingly, he began using more intense swears ever since that.
On a similar note to the above, Captain Sparklez rarely swears in most of his videos beyond anything stronger than "god damnit", and that's generally reserved for his non-Minecraft video. But in his appearance on Web Video/React when the subject was The Farting Preacher, he found out that his theory on the subject was wrong (he had assumed the preacher was a church using viral video as a promotional campaign), and commented "I am so fucking gullible".
And again in "Coffee Tactics". He also throws out the no swearing rule while playing Slender, because he finds it that terrifying.
Fred Clark's Slacktivist blog has a great example in Stop Demanding That You Get Screwed, which has 20 or so paragraphs explaining calmly and patiently why healthcare reform isn't a bad thing, then emphasises it by finishing the postscript with "fuck you, you fucking moron".