Most of the reactions are similar to MindBlinds and lostonearth35, smack him or make a formal complaint. This has happened to me before but in pubs/bars with strangers as I walked past, and my response was to chew them out of it, no thinking required, instant reaction.
This was a distinctly different situation, I was in a foreign country at the time staying with relatives, some I know well, and others not so well. No one in my large extended family has ever behaved this way, perhaps it is cultural and an age related difference, he is an Australian married to my aunt, but I have met him many times before, as a child and in my teenage years. This was out of character. I have doubted a few times since then, that it actually happened!
In all of this I was not concerned for myself, it was not a dangerous situation, I was not physically harmed, alcohol does effect inhibitions, (again not a lot of alcohol) but I was unhappy that this man would make me feel so very uncomfortable. I was concerned for my aunt, at the time I knew that everyone else went silent, except for him. I knew when I looked at her and she averted her eyes, that there was something else amiss.
Ive replayed the scenario a few times since, and the sudden stillness in the room has stayed with me. Like everyone was stunned, or they were holding their breath waiting for my reaction, I didn't react though, not verbally, I think I was stunned. I disassociate/depersonalize in stressful situations, but that is usually in a busy noisy shopping area, or when i experience intense emotions, but in this situation I didn't even know what to feel. I know the thoughts that I was not with usual family members, not in Ireland, in the 'Bush', and no one else was reacting flashed through my mind, and then... nothing.
I think that if there had been any reaction, from anyone I would have perhaps not felt so stunned, or needed to go to bed early.