One has to learn what feels good and what does not and society and our families deem appropriate and what not. Generally, inappropriate, to me, is anything I don't like and let known I don't like or, anything "controlling" (holding you firmly from behind and kissing your neck, without asking or indicating what he was going to do I would deem inappropriate by your grandfather). No, your grandfather cannot kiss you or anyone else who does not wish to be kissed by him; there is no "right" to another's body. He can't hit someone, he can't kiss someone. Generally we give some relatives we enjoy, rights to kiss or hug us, etc. and generally kisses and hugs are gentle and on parts of our body we can "see" what is happening and control the situation somewhat. We're supposed to be "half" of a kiss/hug; anything else is theft/assault/abuse.