What passenger airplane has the lowest fuel efficiency?
TU-144 =  9.78 passenger mpg

TU-144 figures found on another forum, from an official flight planning document:
https://www.airliners.net/forum/viewtopic.php?t=1355819#p19483811

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By comparison the TU-104A = 15.88 passenger mpg

From an old Aviation Week story on the TU-104:
http://aviationweek.com/blog/tupolev-104-harsh-proof-rapid-soviet-progress-1956

Using that article and assuming 0.8 l per kg and 20% reserve, imperial gallons. These figures (especially TU-104A) are rough and would vary by loading and flight profile.