How can I perform the tightest turn possible in a jet?

Solution 1:

Actually the fastest way to do 180° turn is to perform the Immelmann turn.

You just pull up until you're fully inverted, then you do a half-roll.

Solution 2:

Simply put, the slower you're going, the tighter your turn will be. If you need to turn around quickly, you should 1) decelerate 2) roll let/right 3) "turn" (pitch up or down). I say "turn" since jets don't really work the same as a land vehicle and consequently a typical turn is actually a combination of roll and pitch. Even though you can still technically turn via yaw, it's much slower (see this pic on wikipedia: roll/pitch/yaw)