In the original Metal Gear Solid, while in jail, you could do anything you can think of to annoy the guard. "Shut up in there, will ya!!!"
Metal Gear Solid: Psycho Mantis saying the games Solid Snake - no, the player likes! It is also one of the Easter Eggs found before your fight against him, along with the photos of the developers behind him.
Ocelot also does a Fourth Wall banger to the player during the interrogation stage.
Ocelot dropping his revolver while trying to twirl it with his left hand in The Twin Snakes. Especially with how he just stares at Snake for a second like "oh shit" before picking it back up.
In the PS1 version, when Snake sees Liquid walking towards him and Meryl while they're trapped under the Jeep, and just mutters "Uh-oh", as if this isn't the very worst thing that could possibly happen.
From the Gamecube version, the long pause between Snake's "on the battlefield, you never think about what's next" line and the scene fading out. You can literally feel him regretting saying that.
This gem just before Snake's fight with the Cyborg Ninja:
