It's okay if you like your grapes peeled. What you do with your own bunch of grapes is your own business. But what you do in the company of others with grapes on a tray of fruit or in a bowl, is something else. I learned the right way one evening at a friend's apartment in Milan.
We were sitting at her table in the kitchen with wine and some fruit. As we were talking, I was plucking one grape after another off the bunch on in a bowl. When she couldn't stand it anymore, she said, "Yvonne, let me do something here." She took a pair of food scissors from a drawer and furiously cut away the vines I'd left bare and looking like a deer had been at the table. Then she cut the remaining grapes in small clusters so that instead of my grabbing a grape, I picked up four or five grapes in one neat bunch at a time - a much more elegant and sanitary way to eat vitis.
When I serve grapes to guests, I do what I learned that evening in Milan. Not everyone I know was sitting at the table with me so if I'm close enough to the host, I'll ask where are the scissors and offer to help with the grapes. These days with germ phobia in full swing, I am usually thanked. If I'm not a close friend of the host, I say nothing and touch nothing - maybe a strawberry, if not, I'll take my grapes in a glass.