Conventional theories for predicting droplet disruption are based on a dimensionless capillary number and fail when a protein emulsifier is present at moderate concentration. In this study, droplet disruption is examined in simple shear and, in parallel, novel equipment is used to define conditions under which an interfacial stress-transmitting protein network forms at an oil/water interface. Capillary number predictions fail when a rigid interfacial protein network forms. Complete stress-strain curves, to high material deformation, are presented for these networks. This work demonstrates that droplets destabilized by interfacially adsorbed protein should be viewed as deformable capsules or cells surrounded by a stress-transmitting network. Deformation and disruption could their be predicted by existing theories for such systems, using the constitutive data provided by the stress-strain tests. Such an approach is expected to be superior to existing methods based solely on interfacial energy.