There are subjectives, and then there are these. While you may believe a work fits here, and you might be right, people tend to have rather vocal, differing opinions about this subject. Please keep these off of the work's page.
In the ending to Fallout 3, The player must choose to sacrifice either their life or Lyon's in order to activate Project Purity and save the Capital Wasteland. This would be all well and good if it weren't for the fact that three potential party members (a robot, a ghoul and a super mutant) are completely immune to radiation and could thus save the day with no one having to die. (And another potential companion wearing an explosive slave collar, who wouldn't exactlu have much say in the matter.) But no, they come up with an Asspull reason why they can't. Worse, the only way to fix this horrible ending is to actually buy a downloadable content pack that alters the ending to account for these plot holes and leave the player a plot reason for why they can still play after the end of the main campaign.
Bonus headwound points for being too cheap to get Ron Perlman back in the recording studio for said DLC, so you still get called a pussy bitch for having not killed yourself even if you did take the smart option.
The game was actually just about finished before they added companions at the last minute.
Not to mention that by this point you usually have on your person a massive amount of Rad-X and Rad Away. You could walk into Chernobyl with the amount of radiation blocking drugs you have.
The peaceful resolution to the "Tenpenny Towers" quest. Roy ends up killing all the human tenants anyway later on. This in itself is not a Wallbanger, as it fits into the Crapsack World that the postnuclear-apocalypse world is. The Wallbanger is that Roy is still listed as a Good character by the game, meaning you lose karma points if you kill him afterwards in retaliation for the murder of all the occupants who had voted to let him in.
Not to mention 3 Dog bitches at you for killing him. Besides he's only a "Good" character because Karma =reputation, and Roy has one helluva good rep from 3 Dog.
3 Dog bitches for killing all the innocent ghouls who were living with Roy in the Metro Tunnels instead of moving them into the tower.
An early part of Fallout 3 add-on pack The Pitt could be considered a Wall Banger. Three options are open to you when first entering The Pitt Downtown. First, you can put on a slave outfit and pose as a slave; Mex, the main guard, will strip you of your gear. The second option is to claim you want to join the Raiders. The third option is, predictably, kill the guards and sneak in. The second and third options drop you right into an ambush, four Pitt Raiders armed with Police Batons will beat you unconscious and take all your things, leaving you with a Tattered Slave Outfit. Why is this a Wall Banger? Because there is absolutely nothing to stop you from entering while wearing Power Armour that lets you go toe-to-toe with the likes of a Super Mutant Behemoth (a 20ft tall muscle-bound monster armed with a fire hydrant - yes, you read that right) and come out on top, survive direct hits from missiles and be tough enough to stand in the middle of a bunch of fragmentation grenades with nary a scratch, and carrying enough weapons and ammunition to worry God. And yet, even when you're enough of a Bad Ass to wander right into the bunker held by a multitude of heavily-armed bloodthirsty mercenaries and slaughter the entire lot of them, you are beaten into unconsciousness, unable to fight back, by a few burly idiots with maybe 150 uncontested IQ points between them who are armed with sticks.
Which gets even better if you're wearing Chinese stealth armour, which turns you invisible, so even while they beat you to unconsciousness, there's still a message at the top of the screen saying you haven't been detected; i.e. they don't even know you're there and just decided to wail on a doorway in the hopes an invisible person might be standing there.
And when you get enough "cred" to be given your gear back after winning the arena fights (for some reason the Raiders haven't split it up and sold it yet, and trust you enough to give it to you despite suspecting you of causing a slave rebellion) you can go on a Raider-killing rampage. You can kill everyone, even the top-guards, without breaking a sweat. It is not explained why you had to be so cautious at first when you end up killing them all in a massive rebellion anyways.
Little Lamplight. There's a town full of nothing but children under 16. Okay. They kick teenagers out when they turn 16. Less okay. You have to go rescue some of their friends from slavers before they let you in. Less okay, considering that the entrance to their town is a plywood gate guarded by a prepubescent boy with an assault rifle, and the player has access to things like flamers and miniature nuclear weapons. In real life, the player could just grab the Mayor from his post near the gate, pull him outside, and hold him hostage until someone else opens the gate. However, all the kids in Little Lamplight have plot armour, except the one who's just turned 16 and is forced to head off to "Big Town". Leaving aside the question of where the kids all came from in the first place, there's a whole slew of Super Mutants on the other side of the town, all of whom are, like the player, equally unable to get past that plywood gate without assistance. To sum up, we have a town of invincible children from nowhere, surrounded by heavily armed slavers and Super Mutants on both sides, none of whom are able to get past a pair of flimsy plywood gates constructed by the aforementioned children. Did I mention that the kids are all rude and arrogant, precisely the sort of people the PC would want to kill if only they weren't invincible?
The developers actually intended the secret of where the children of Little Lamplight came from to be ambiguous, though one could surmise that since teenage girls can still get pregnant by 16...of course, leaving a giant open question like this is a Wall Banger in and of itself.
The fact that Caesars Legion never under any circumstances ends up backstabbing a female Courier after they have won control of the Mojave. You could maybe make the argument that their entire army is scared witless of a power armour equipped walking tank capable of killing Deathclaws with her bare hands (although that never stops them sending Legion hit squads after you if you side with the NCR) but even if you speed run the game as an under-equipped pacifist armed with a selection of small knives do they consider it. Remember this is a group of men who find raping, beating, enslaving and killing women as entertaining and normal as you or I would watching television... and they apparently never find the prospect of claiming your young nubile body as their victory prize appealing? No dice.