1. Psycho Rampage. Turn on invinsibility and infinate ammo, and go to a level with re-spawning enemys and just sit there blasting them as they come along, it's even more enjoyable with all guns, therefor you can use thing like: AR33s and mines.
2. Taunt Natalya. This is cool. Go to a level where Natalya is quite strong like the jungle, control etc, and literally taunt her, slap, shoot and throw knives at her it's almost humerous!.
3. This is pretty good go to the facility and slap a scientist so he draws a gun, when he starts shooting/throwing grenades dodge them and slap him some more.
4. Go to the Facility turn on invins, all guns and infinate ammo, go to where Trevelyan is, wait till he sounds the alarm, kill Ourumov and pull out your RCP-90 and mow them down as they come down the stairs.
5. Turn on all guns invins and infinate ammo. Now all you do is act like a real spy using all your arsenal against them, try to be as quiet as possible without anyone seeing you; you must become familiar of all guards posts and the route they take when they're patrolling. I've done this without being seen, except for when talking to Mishkin and picking up Nayalya.
6. Turn on enemy rockets and go to the Dam, go into the start of the tunnel and let the guards at the other end shoot at you and dodge their rockets as they come to you. (for even more fun, put 007 mode on with enemy accuracy at 100%, this way every rocket is aimed at your head!)