Was from myreadingmanga but it might be on here as well. It involved lots of school students being locked up in the school gym, then it ends with them all forming a sort of fuck-train. I used to send the images to my school mates to terrorise them, but I've lost the images now and I can't find it anywhere.
The fucking funny manga derp faces during it and the normal ass conversation afterwards got me fucking crying. Old school yaoi truly is one of the seven wonders of the world.