If you want to see negative dihedral, try a Jet Ranger with fixed floats in autorotation. The huge area under the CG (the vertical position of the CG) will give you negative dihedral - apply left pedal, and you'd expect to roll left in most helicopters. In the 206 with fixed floats in autorotation, adding left pedal will cause the helicopter to yaw left, and after pausing for two marching paces (as my drill instructors used to say), it will roll right. Negative dihedral.
Seen one other time in a very light (i.e nothing in the machine expect a slave radio, brand new off the production line) Bell 206L3 with high skid gear and fairings on the crosstubes. Fairings are not used on the crosstubes any longer if I remember correctly.