The fastest speed imaginable...light speed is too slow! It is extremely dangerous to go to ludicrous speed. It may result in you going to plaid. Also, going from ludicrous speed to a dead stop will result in you being launched across your ship, flying straight into a wall.

A phrase describing something that happened or took place very quickly.
Preferably shouted when drunk with your closest group of friends.

Think of the fastest speed imaginable, so fast that it is impossible to see. Now times that speed by 12 and you get ludicrous speed.