Play the half life series and portal series in This order:
Half life 1
Blue shift
Opposing force
Portal 1
Half life 2
Half life 2 episode 1
Half life 2 episode 2
Portal 2
Half life 3
Play the sims 1 or 2 and just mess around with what the games have to offer
Play Ut2004, grab some soundpacks and skins, get the ballistic weapons pack, get TDM 4 and CTF 4 and forget around. There's this Tony Montana soundpack and I applied it to a bot, I then kept hitting the bot with a knife and it was getting pissed off, it was hilarious. Ut2004 is crazy, you can even get Beavis and Butthead in that game. Its one of the best games ever
Play Mugen, its free and has tons of downloadable characters. Much like UT2004 but in a Super smash bros brawl 2d style, the game can give you a laugh sometimes. There's a Hotel mario character that you can download and its hilarious to hear when it talks.
if you have gmod then get some NPC and NPC weapon mods and create a giant NPC war in gm_flatgrassconstruct which can be downloaded form the workshop. I have spent other 2 hours by making NPC wars in gmod but only do it if your PC can handle it
play TF2 MVM, even the boot camp is time wasting at some times or play tf2 ctf. Sometimes on tf2's ctf there are servers that end up taking hours to decide the winner, thats how I've spent hundreds of hours on Tf2 and by playing mvm on it as well.
