The opportunistic omnivores in the office will eat anything we leave unattended in the kitchen, and now those opportunivores have eaten all the Christmas cookies.
That opportunistic jerk took all the free condoms from the clinic, they're such an opportunivore.
Someone following the "high-everything diet", i.e. high-fat, high-carb, and high-protein, without any restriction on calories or macro-nutrient ratios. Could be a competitive eater, big body-builder, or just a normal person who will eat anything.