a Crotch rocket has taken on several definitions:
1) a very fast motor cycle, either foreign or domestic that one must lean forward on while riding thus making it look like a rocket is being stratled between ones legs.
2) an erection so hard that it can be somewhat painful due to the extreme arousal or amount of blood in the penis.
3) a vibrator, usually metallic or metallic in color.
1) like my crotch rocket? i pay more in insurance per month than the payments of the bike itself!
2) certain erection giving pills can give men 4 hour long crotch rockets.
3) my friend got a new crotch rocket from the adult novelty store.