Assign your Rapid button to both RB and Y. This can be done by holding the turbo button and pressing both RB and Y at the same time. When you're in game, pick a class with semtex. Turn on the turbo fire button and Hold RB and Y Have fun annoying others.
*NOTE* - If done too long it can also end the game! The message will say : "(The down button) G_Index entities"
Best if done with a partner.