Unreal Tournament III

NOTE: As the servers are down, this is now unobtainable.

This is the only trophy that truly requires online. This means that it is now unobtainable due to the server shutdown. It could have been done in approximately 8 hours if done actively, but could also be done automatically if you wanted to leave your game idle.
This is how you would do it:

Active Method

Suggested Setup
Gametype: Deathmatch
Map: Rising Sun
Mutators: Speed Freak, Weapon Replacement (All to Enforcer)
Kill limit: 5

Playing with this setup you should be able to finish most matches in as little as 10 seconds. As soon as the match starts you are going to want to get over where the Bio Rifle regularly spawns (under the stairs beside the body armor). All the bots immediately congregate there, so if you've managed to pick up a second Enforcer along the way you can very quickly take out 5 to win the match. When it shows your player and says you've won repeatedly tap to skip to the next match. Continue doing this and you should be able to finish this trophy in approximately 8 hours of actively playing.

Automatic Method

Suggested Setup
Gametype: Team Deathmatch
Map: Rising Sun
Mutators: Speed Freak, Instagib
Bot Level: Skilled
Kill limit: 10

This setup basically gets the best average win ratio for a team of bots playing automatically. If you leave your controller plugged in the game will run continuously with the bots playing and winning matches. Since this method is random there is no guarantee on how long it will take to reach the 500 wins, therefore it would be advised that you play actively if at all possible and leave the game running with this setup if you have to leave your game. Make sure that you do check it every once and a while though if possible, as I found the game froze a few times while doing this, and if you are signed out of PSN at any time you are automatically booted back to the main menu.