Manual transmission designed with straight cut gears and no syncronizing rings.
The original GT-40's 5-speed
The word derives from its two combined words Crash and Box. To Crashbox is to Crash the Box or Dive in the muff. When referring to person it is someone that is highly skilled in getting in a woman's pants.
Man I have to say taking home two women from that party last night made you a real Crashbox.