The class which can gain the lowest AC is the Blade.
Defensive Spin -10 AC
Big Metal Unit -10 AC (Pantaloon Armour), sets base AC to -10 AC
Ring of Gaxx -2 AC
Ring of Earth Control -1 AC
Helmet of Defence -1 AC
Cloak of the Sewers -1 AC
18 DEX -4 AC
Blur -3 AC
That's -32 AC for you.
It only works as -20 AC though.