56s thing is pretty well known.
I always thought the worst hand vs AA was A9o with the 9 suited with the A.
http://twodimes.net/h/?z=147098
pokenum -h ac ad - kc 2d
Holdem Hi: 1712304 enumerated boards
cards win %win lose %lose tie %tie EV
Ac Ad 1538197 89.83 165043 9.64 9064 0.53 0.901
Kc 2d 165043 9.64 1538197 89.83 9064 0.53 0.099
http://twodimes.net/h/?z=424554
pokenum -h ac ad - ah 9d
Holdem Hi: 1712304 enumerated boards
cards win %win lose %lose tie %tie EV
Ac Ad 1598785 93.37 89199 5.21 24320 1.42 0.941
9d Ah 89199 5.21 1598785 93.37 24320 1.42 0.059