I think this is personal and is going to always depend on the receiving person. If they took an act of kindness as bragging then I guess it is. But I think if I saw a friend on a flight and they sent me a drink I would think it was nice. But then I'm not bitter and can buy first class tickets if I really wanted to I just don't think it's worth the extra in many cases. Also, I can't help but wonder if the acquaintance was a man and it damaged his fragile ego.