Imagine this. Your OC (original character) comes home after a long night out. He/she/vice-versa leaves their leftovers from dinner in the fridge over night...
When they wake up, they find their roommate gobbling their leftovers.
Your character is shocked, stunned, utterly, flabbergasted, appalled, speechless, staggered even, bewildered, aghast, and overall gobsmacked.