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 them in, with reflecting walls. What happened? 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, almost always by Lewis. Though he is usually a victim of his own impulses and poor planning, he is also cursed with truly awful dice luck. This is a decent example of how bad Lewis 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 50 trillion.
Helix managed to blow out a bulkhead on the spacecraft he and Sam use. While making microwave popcorn, no less.
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.
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.note Of course, because the Stable Time Loop required them to fail, so in this case, Epic Failure Is The Only Option.
Eridan's entire session in the Land of Wrath and Angels was wasted due to his determination to kill the friendly yet formidable angels until he finally turns them all against him. Everyone he complains to about it figures out that they aren't the enemies, but he continues to whine about its unfairness long after the game is over.
There's a ton of examples from VG Cats. In one comic, Leo (who is Altair from Assassin's Creed) tries to pick his nose, only to stab himself in the face with the hidden blade.