Of all the genres I would choose if someone held a gun to my head and forced me to make a Seinfeld video game, I can't say a first person shooter would be high on my list. But hey, that didn't stop Doug Keener from trying that very thing using Doom II, and dammit he has done a fine job.
Apparently taking over a hundred hours of work, this .wad file lets you wander around Jerry's apartment from the '90s hit sitcom, Seinfeld. Complete with custom sprites, textures and a few clips of famous one-liners from the show ("These pretzels are making me thirsty!") it's pretty bizarre watching lo-fi Seinfeld characters amble around.
The attention to detail is amazing, as you can see for yourself in the video that Doug Keener uploaded to his YouTube channel in order to show the mod off. Not going to lie to you though, I definitely flinched a bit when he pumped a round into poor George. For the briefest of moments, I was alarmed to remember that Doom 2 is actually supposed to be...y'know violent.
Anyway, if you want to see for yourself you can download the .wad from a Google Drive link provided in the original posting on the Doomworld forums. Obviously you'll need a copy of Doom 2 which you can grab on Steam for $4.99/£5.99.