The underwear bomber did not buy a one-way ticket to Detroit. The Guardian reports:
Nigeria's civil aviation authority said last night that [Umar Farouk Abdulmutallab] bought his round-trip ticket from Lagos to Detroit via Amsterdam at a KLM office in Ghana's capital, Accra, on 16 December, with a planned return of 8 January. He paid the £1,775 fare in cash. Before the flight departed on Thursday, he checked in as normal, taking only a carry-on bag.
Al-Qaida Links To Christmas Day Plane Bomb Plot Investigated
Hopefully, if enough people repeat this, we won't hear about this particular urban legend anymore.
Consider this my public service for the month.
UPDATE: More public service: click here, this video is hilarious.