This trophy along with some others tend to be a bit buggy. There are grapes in the 1st drawer of the fridge in the kitchen area of the garage. Simply pick a few grape and throw them towards your mouth.
It took me quite a few tries as it must register strangely even when you hear Tony chewing.
I tried a variety of methods of launching it up towards my face and straight in the air and physically moving my head to catch the grape to get it to unlock.