A Running Gag in 8-Bit Theater is the phrase "[situation] is X, X forever!" (e.g. "At last that Hell Door is vanquished, I'm safe. Safe forever!" — Black Mage, on getting past a door which was constantly opening and closing). Characters who have uttered these words always suffer in some way or other (for example in the last example, Black Mage was immediately attacked by the personification of Thief's greed.
"And now we're safe forever" is a Running Gag in itself, usually said by Red Mage right before something calamitous occurs. Near the end of the comic, he says they're "...safe forever. Again." while super-evil orb-charged omnipotent jackass wizard Sarda appears in the background, preparing to kill them all. Again.
Also the gag of a character or characters saying something sickeningly ideal, often about how life finally stopped sucking for them, before they get hit by a Hadoken or a meteor or something.
Schlock Mercenary has made this into an inside joke. The entire cast isGenre Savvy and refers to doing this as "taunting/invoking Murphy". Every time a character tries to say "What could go wrong?" or "It's a guaranteed success" or the like, he/she/it/they is violently interrupted. It's generally foreshadowing that something will go wrong, but that's a sucker bet anyway.
Der Trihs: Trouble, sir? What kind of trouble could they -
Goblins has a sub-comic called Tempts Fate after the lead character, Tempts Fate. Why is he called that? The writer decided to have people's donations actually do something tangible, so he set up Tempts Fate as a sort of arcade game: if donations reach a certain goal by a certain date, Tempts Fate will pass the obstacle in his way; the more the donations exceed the goal, the more awesome Tempts Fate's victory will be. If people fail to donate enough money by the deadline, then Tempts Fate will fail, and die, and live on only in our memories.
And so far, Tempts Fate has lived through 8 challenges in spectacular fashion. So much so that the author has added extra properties to the donations, including a sort of "dice" modifier based on the cents digit that decides which cool item Tempts Fate gets if the biggest goal is met.
When he offered T-shirts for donations during the "Tempts Vs. The Really, Really poorly Made Characters" challenge, the donations skyrocketed, collecting more than enough for the fourth and final goal before the first goal's deadline. The result? Tempts killed the poorly made characters so hard that it killed the people playing those characters (except Elfgirl, as she didn't want to kill him or, indeed, even play D&D, so he just let her go; he killed the DM instead).
Old Prisoner: HA! I knew I made the right call staying in prison. That Tsukiko chick is getting her ass kicked by an elemental! It's so much safer up here! Tsukiko:SHOUT! (cell crumbles, a slab of stone falls and crushes the old man to death) Nale: Well, now, really, what did you expect after a line like that?
Art: If I had to run away from something right now, I'd be so screwed. (...cue Flying Trashcans who came all the way from Mars just to get him)
Lampshaded in Narbonic: the characters are stranded in a raft at sea, with no food, no water, and no cigarettes, and Dave starts to say it couldn't be worse. Genre savvy Mell tries to stop him, but as the huge wave looms over the raft, Helen points out that it's too late. Dave's last words are "Well, MY face is red."
This strip of Dominic Deegan. Lack of scrying alerts aside, you would think a seer who has been through as much crap as Dominic has would know better than to even think the words "Nothing bad will happen."...
To be fair, we find out later that "the bad thing" actually blocked his second sight so that he — nor any other seer — would spot him coming.
Fate launches all salvos in this strip. Also combines a "Things can't get any worse." statement with a response in the next panel midsentence. Either Dominic needs his crystal balls polished or he has a really twisted definition of "Nothing bad will happen."
Dan: Ha! Shows what you know, universe! Trying to bury me with girls only makes everything better!
Also in this comic, where Mab actually isn't sure if the next event to happen makes anything better or worse.
Homestuck likes this one. Due to the high number of playable characters, the narrative is prone to sudden shifts in perspective, often at key dramatic moments. The fate-tempting is mostly hanging a lampshade on the whole affair.
Played with in Hellbound; mostly used straight, occasionally subverted, the best one occurring fairly early on:
Guy: At least things can't get any worse.... (silence) Baxter: Hey, nothing happened! I guess your life can't get any worse than this! You've hit Rock Bottom, but at least nothing else can go wrong! Guy: Oh good, my suicide shall go flawlessly. Baxter: That's the spirit!
Parodied one strip when Torg and Zoë are racing K'Z'K to the Book of Güd. (More specifically, Torg tries to invoke the opposite version — tempting fate to do something good — before Zoë mentions tempting fate the usual way, and that works.)
There's a pretty over-the-top one early on.
Riff: I can fetch him back in a few hours. Torg will be fine as long as he didn't get zapped to a "Dimension of Pain" or something. (meanwhile) Demon Lord Horribus: Welcome to the Dimension of Pain! Torg: Thanks! Can I use your restroom? Horribus: Nope.
Gunnerkrigg Court, Chapter 23 has an interesting variation on this. During the camping trip, students start mysteriously disappearing, and the remaining students deduce that it must be a prank the teachers are pulling. They come up with a plan to find the missing students and expose the prank, but it requires one more student to deliberately get kidnapped. Kat volunteers, because she's cool with being kidnapped by Mr. Eglamore. Cue Kat, sitting by herself, announcing to no-one in particular, "Oh boy! I sure hope nothing happens to me now that I'm here all alone!" As expected, she immediately gets kidnapped... but not by Mr. Eglamore.
Yahtzee Takes on the World adds a bit of spin by showing a flying saucer crashing into the characters' lair before it cuts to a very annoyed Yahtzee, who announces "As I was saying, it's nice to get back to normal."
In Something Positive, one of Davan's friends says that he won't have a costume unless they have one in a can waiting for him. They do.
In a recent strip, Sheila asks "how hard can it be to catch dumb plant-eaters" while planning on hunting in Kell's place to help her meet quota. Suddenly, an icy cold blast out of nowhere freezes all the vegetation.
Dechs:(while waiting on a rooftop for something interesting to happen) I'm bored. (pause) Dechs: It seems like a quiet night. (pause) Dechs: I said, it seems like a quiet night. (nothing happens) Dechs: Well damn, that usually works.
The commander of the heliolux airfleet (communication systems/roasting) after being informed that contact with several units was lost mid-sentence and then the contact with a bay of their own ship is lost right now. She couldn't finish the next sentence with anything better than "We'll miss the fighting!". Cue a Jägermonster walking in right behind her and happily screaming "Wrong!" (Jorgi likes to be contrary).
Xerxsephnia makes a very foolish assumption that she has Agatha helplessly grounded, far away from her town or any potential allies. When her brother tries to persuade her that "the Heterodyne Girl" is a thread after all, she brushes his concerns off, assuring him they are not in a Heterodyne Play and asking "What can she do?" Cue Agatha flying past the tower's window in a swan-shaped sleigh.
Marlene: What? Why— Ivy, how is it that you always pick the most ironic moments to ruin my life? Ivy: Oh no, did you just get done saying that everything was back to normal again? Marlene: ...No... Ivy: Yes you did. I know that tone of voice. Why do you keep doing this to yourself?
In A Miracle of Science Caprice says "We're perfectly fine" right before her ship is attacked by the weapon from which it got no protection. And repeats just before it explodes. Benjamin shuts her up before she says this the third time. Though it was after he taunted killer bots himself.
Also, Vegetto during the lunch break. He's certain he won't need to face Broly, because the maniac'll break the rules and get sent back... guess who gets chosen as his first opponent?
Cade and Sam in Modern Day Treasure Seekers talk about how rickety the mines look, and the possibility that any booby traps would have stopped working after being there for many years... immediately before triggering a trap.