I was wondering if anyone knows the name of this fic. Basically what happens is Engineer joins and he finds out that none of the team members can touch each other (himself included). I guess the Administrator made it so nobody would fool around on the team. And Demoman and Engineer later find a way to work around that. It's been bugging me for awhile because I thought it was quite good.
I don't know if there's one with Demo, but "Asymptote" by renquise has that premise with Engie and Spy!