The origin of the term is lost in the past... but many theories about its origins exist:
1. SQUirrely kID
2. soft tissued creature (i.e. no gear)
3. a creature that accellerates rapidly in straight lines, but must slow to nearly a stop to negotiate a turn.
4. someone who can't control their bike properly, and so flail their appengages behind them as they rocket by (like a squid)
many more exist, but they all mean the same thing... a jackass on a bike with too much ego and too little skill/gear.