Black Mage finally gets into a strong positionto kill his hated allies, as he has attempted many times before. To assure his success, he aimed his Kame Hame Hadoken not at them, but at the volcano they're standing on, which he plans would cause it to erupt and kill absolutely everything in the local and not-so-local vicinity. But, as the universe's Butt Monkey, he fails. How does he fail? He misses. He misses an entire freaking mountain. He misses anything on the entire planet and ends up killing the dinosaurs.
Thief: Not that I'm complaining about it, but... HOW DO YOU MISS A VOLCANO?!
Earlier, when they were captured, BM tried to kill his allies, it was in a small corridor, easy to hit, reflecting walls. What happens, he hit something, himself. It was the same attack as the volcano.
"How did you not only manage to miss us, but also hit yourself?"
Due to Red Mage's unfailing belief the world works like a Tabletop RPG, this occasionally comes up for him, too.
Black Mage: You pushed Red Mage [...] Onto Fighter's sword. Fighter: Which is weird because it started out sheathed. Red Mage: I botched my Athletic Roll...Big time...
Sarah: And it was eligible in the first place because...?
Gary: Well, we needed a fourth.
One time Fighter lost a game of Drownball. He spent several minutes underwater wearing heavy armor, yet...
Fighter: I did a thing where I didn't drown.
Then there are both of Black Belt's memorable attempts to find the bathroom.
With all these examples, it's pretty safe to say that 8-Bit Theater could alternatively be titled Epic Failure: The Webcomic.
Aaron Williams' Full Frontal Nerdity has, among other delightful slices of Gamer Life and other nerd instances, the occasional example of truly epic fail for the everyman. This is a decent example of how bad this guy can roll. He has also jinxed a die so badly it infected other d20 with the "1" virus, rolled a "1" when it was buried, and started making "1" show up everywhere. Further, Williams even has a collection of Nerdity out titled the Big Book of Epic Fail.
Matt from Murphy's Law did this on his Test of Hidden Traps.
In the first book of Goblins, Fumbles fumbles a to-hit roll spectacularly. He trips, sends his spears flying into a lantern, which sets a hut on fire, which sets a bird on fire, and said bird retaliates by gouging the hell out of Fumbles' head.
Forgath: I just wanna know what kind of fumble chart he's using, so I could avoid it.
In a non-canon Problem Sleuthdonation page, Team Sleuth strikes back at the Midnight Crew with the insanely powerful Catenative Doomsday Dice Cascader, a weapon that calculates damage by rolling a die for result X, and filling the remaining popomatic bubbles with additional X-sided dice. This is repeated until all dice are rolled, with the final die determining damage. The final result? One. Out of Fifty trillion.
Helix managed to blow out a bulkhead on the spacecraft he and Sam use while making microwave popcorn.
Stef Murky of User Friendly is absolutely awful at video games. He once fell in the lava in Neverwinter Nights (something not possible without modding the game) and also once fell in the lava at the startup screen of Quake II.
Cleo from Bobwhite discusses this. While her dad tries to teach her how to fold clothes, Cleo talks about how funny it would be if her terrible clothes-folding skills accidentally set her clothes on fire.
Thog failed his will save against a Zone of Truth spell (which normally only prevents telling lies) so badly that he started spouting every truth he knew, resulting in several Too Much Information moments.
The Ho'aku tribe in Survivor: Fan Characters was truly an epic fail, filled with a) weak and easily influenced members, b) jealous and power-hungry contestants who wanted to lead and voted out the first two leaders, and c) Russell Hantz, who sabotaged their tribe. What happened was one of the worst losing streaks in the comic's history, with the Ho'aku tribe losing ten out of thirteen challenges, going to every single Tribal Council but one, and ultimately being whittled down to two members. However, the tribe's plight is spectacularly subverted when a member of the Ho'aku tribe manages to go on an immunity run and win the game!
Cherman from Season 9 was an epic fail in all challenges, in spite of being a robot specifically programmed to be the ultimate Survivor bot. Then it's similarly subverted at the very end when he wins the entire game.
xkcd: These twocomics. Failing to throw a boomerang correctly is one thing. But this guy eventually managed to throw it so badly he broke the ozone layer.
In Homestuck, a certain unwise action in the Kids' session lead to consequences so staggering they rendered someone else's session of the gameunwinnable.
And then it turns out that it was someone in the other session who rendered both sessions unwinnable... by giving a universe cancer. Fails don't get much more epic than that.
Earlier, Aubrey makes a TV show. When it's broadcast, the State of Massachusetts imposes a restraining order on her to keep her away from any TV or film-making equipment in the future.