If you pretend that other players are NPCs, you can larp a simulator of enraging people. Ranked from awkward silence after a horrible quip, up to lines upon lines of abuse in broken english. Bonus points for ragequits and rants on how callvoting during a game should be an option.
it should be an expanded version of training mode, so if you pass the 2 existing maps (rl [including the secret room] and strafe jumping) it counts as if you passed a stage/challenge. The third map could be raz_trainqlbeta3, and the 4th map strafe pads.
Also it should have some defrag maps which you have to finish before the time runs out, and hopefully having to do flag runs in current maps (just add a counter), even better if they add examples for both in the form of youtube videos.
That is absurdly easy to do and, if done correctly, it can lead to a great singleplayer.
example: add 4 medals, so you can just pass the map and it counts as bronze. Pass it faster so you get silver, and if you are very good (5% or less of quake players) get a gold. Platinium goes to an insanely fast time, or by completing the 8th strafe pad line and so on.