Played straight, and then lampshaded in this chapter of a Warhammer 40,000 fanfic, which has the main character bash an Eldar Farseer and Space Marine Terminator with a fire extinguisher in much the same way as he did the previous chapter, gives a snark about the possibility of it becoming a running gag, then goes on to extinguish the smoldering lampshade behind him.
Chapter 8 of Takamachi Nanoha of 2814 by Shadow Crystal Mage makes fun of this trope, repeatedly having characters ask where other characters want lampshades hung, or variations thereof. It also plays this trope straight, sometimes in the same paragraph as the gags.
A Very Potter Sequel has a (seemingly) improvisational instance of this. There is a scene where Ron attempts to pull a poster of Taylor Lautner off the wall in Umbridge's office, but it appears the actor has too much trouble trying to tear it down and ends up returning to the group, saying "it's stuck on with magic!" When they appear in the next room — which is the same area on the stage they just "left" — they comment on the fact that "there's a Taylor Lautner poster in here, too!"
In thisGlee fanfic, Rachel pretends to be a boy so that she can enroll at Dalton, and ends up being Kurt's roommate. Upon finding out that she'll be rooming with the only person in the place who is in on the secret, she says: "Oh. Well, that's ridiculously convenient."
Obsessive Lily Disorder The story is set in the seventies and Sirius is singing a lot of more modern songs. James points this out:
"Sirius, for Christ's sake," James sighed, "Will you ever stop singing random songs that probably haven't been written yet and are completely out of this time period?"
In Fantasy Sports League: "It's unprecedented! In the history of literature and sports I don't think there's ever been a case where a group of ne'er-do-wells were able to band together and in the most unlikely of conditions, take on an all-powerful foe! This is amazing!"
Those Lacking Spines is, without a doubt, the single most lampshade-riddled fanfiction ever. It takes the time to bring up anything and everything ever done by a fanfiction writer who wrote about Kingdom Hearts and Organization XIII, and proceeds to mock it and deconstruct it in every single way possible.
When Terra expresses surprise that Jump City has a diamond mine, Cyborg states that the city has a lot of stuff, and that he sometimes still gets surprised. This most likely is in reference to the fact that the city's layout on the show often seemed to change depending on the needs of each episode.
Jinx at one point wonders why buildings always end up on fire when they're attacked by villains.
—Buford: Ugh! How come whenever someone is about to say something important they get cut off? That gets annoying.
The Ranma ½Elsewhere FicBoy Scouts ½ has a charater, Bill Gelinas, who has developed a strange knack of pointing out when things are too convenient, or of thinking that he sees unlikely patterns in the lives of himself and his fellows. His declarations of such have even developed a stock response of, "Shut up, Bill!" that has been so ingrained in his fellows that they have been known to shout it out almost like a Pavlovian response even if Bill is not present when something too convenient occurs. (Or, to reallybreak the fourth wall, on rare occasion a scene with such an occurrence without him present has cut away to him for him to randomly declare the convenience of something he'd logically not know is happening.)
Also used to dramatic effect. Why exactly do the super forms need 50 rings? And if you used more than one ring a second, do you get some sort of power boost?
Bystander: "Cinos? It's Sonic spelled backwards! Cinos is... evil Sonic... Because he's... Cinos. Who comes up with this stuff? I'd expect better from a teenager's first attempt at a novel!"
Navarone spends half the story lampshading events in Diaries of a Madman, from the strange nature of the world, to the crazy nature of Equestrian villains. He's also quite fond of ranting on about the inexplicable uses of hooves ponies are capable of.
You can trust Discord to get a major one in for the Triptych Continuum (even if you can't trust him for anything else), complete with appropriate accessory. His description of the mission in the main story comes out like this: '"You're going to go do something that I, with all my power, could seemingly accomplish all by myself with practically no effort on my part. But instead, I'm sending a bunch of considerably lesser strengths out there for reasons which I will not explain and allowing my quasi-omnipotent self to take a nap while everypony else deals with all the trouble." He glanced back at Celestia, adjusted the lampshade resting on his head. "That's about right, isn't it?"'