Then I would try again, and next time not so gentle ; )
But seriously, why not just flag down an FA and let them deal with it?

That looks really bad. It is hard to believe that people behave this way but some of them do. I think I would have gotten the FA involved, although when I was younger I probably would have put up with it.

Recently I had two incidents. In one, a young and very thin woman sat next to me in coach in the middle seat on a short flight within California. She contorted herself to sort of curl up in her seat, with her feet all the way up on the seat, ending up facing either me (window) or the person in the aisle seat, and proceeded to nap with an eye mask on. She intruded into my space several times and finally when her foot ended up on my knee, I asked her politely to fix the situation. She did so in a polite but annoyed fashion and continued with the contortions throughout the flight. My guess is that she came in from a flight from Asia and was jet lagged but still it was annoying and socially inappropriate.

I had an even more unpleasant experience on a flight in domestic J (flat seat) with a very entitled middle aged man (my age!). From the moment he arrived, he took up more than his share of space in a metaphorical sense, acting very agitated and huffy and using up the entire shared table for his boarding pass, iPad, glasses—whatever he cared to toss there. The best way I can describe this is that he was going out of his way to encroach in a dramatic fashion, sort of inviting a confrontation. After this had gone on for about an hour, he put his drink down on my side of the shared table when I had picked up mine, meaning I had nowhere to return my own drink.

At that point, I told him very bluntly to keep his belongings on his side of the table. He then began to have a temper tantrum, which I ignored other than to ask him to have some common courtesy. I was about to call the FA when he calmed down. He behaved for the rest of the flight and seemed somewhat embarrassed. He was steadily knocking back drinks in flight and it later occurred to me that he may have been drunk when he arrived.

95% of the time, a very minor comment or glance is sufficient to deal with situations like this but when it goes on, the direct approach is necessary.

Some folks are unaware of their actions and others are fully aware people are non confrontational. You paid for your seat and space. Maintain your borders by demanding your space. They may be pissed but not your problem,

Thats where you pick up the drink, bring it up front to the FA and tell them you're all done with that one. Or call the FA over and give it to them.