Up to (and including) Ocelot. This fight has been broken beyond recognition.
For those of you unfamiliar with this boss fight, the process goes like this: the guy in the middle, Kenneth Baker, is trapped in a plethora of Semtex. If Snake crosses the yellow line, the C4 activates, killing Baker and triggering a Game Over. Ocelot will fire his magnum shots, and you're supposed to dodge them and then shoot him while he runs away to reload.
I stand where I do in order to exploit a safety measure programmed in Ocelot's AI: Ocelot can never shoot or kill Baker, and if one of his magnum bullets looks like it will bounce off a wall and hurt Baker, it doesn't. Therefore I can stand in one place and fire at Ocelot on his optimal vulnerability frame while he barely misses me with his magnum EVERY SINGLE TIME. Of course, I lose some time when compared to the SDA run by not being able to shoot him optimally while he reloads, but the overall fight is faster. This method also saves a stun grenade, saving me another 10-15 seconds by not having to backtrack to the north side of the B1 entrance and grab some.