Okay, so I have a suggestion for a challenge.
In the original Timesplitters on PS2, if you go to the multiplayer option there is a very tiny map called "Tomb". Given how tiny the map is, once you load up that map with the maximum number of bots, absolute chaos ensues (And Timesplitters is a very fast-paced game as well, so it's quite fun). You're allowed to create up to four teams; my suggestion is that each of you must create three different teams of three bots, place yourselves alone on your own teams, make the scores unlimited, set a time limit, and give the point to whoever gets the most kills (You can't play it online, so my suggestion would be to just play against bots on your own and compare scores at the end).
It's worth noting that, if you guys aren't familiar with the game, Timesplitters boasts an absurd amount of options, including choosing seven total weapons to use out of all the weapons in the game. You guys have two options here: You can experiment with the game and see what might work best in terms of either balance or chaos, or you can just jump right in and pick whatever sounds cool.
Also, I'm pretty sure "Tomb" is the first map in the game, so you don't need to put any work into unlocking it.
EDIT: I'm not sure if every weapon is available for multiplayer at the start of the game; if it's not, the campaign takes a total of about two hours to beat on easy mode, so that shouldn't be too much of a problem. But I'm pretty sure all the weapons are there from the beginning.