if someone asks you

'You are even more beautiful than the last time I saw you but I can't put my finger on what it is'

it's one way to get away with it if they really insist to put you on the spot

Quote from dong-thefirst

if you notice anything new or different, is it acceptable to say they gained weight?

I would simply respond with: “Why? does it matter?”

Idk, sometimes gaining weight can be a good thing but other times its a little not nice

Even if it was technically true, weight is a rude thing to mention that circumstance as people tend to be more senstive about it, More so about gaining weight so no. However losing weight can be deemed more complimentary although depends on how you say it.

Easier to say you don't know, and let them proceed to tell you, save feelings and time lol

I wouldn’t make a comment to be completely honest. I think it would be a little rude to say that they gained weight, unless that was a goal of their’s, but even still I would be a bit uncomfortable answering that. I don’t think weight matters, but I understand that people sometimes want to gain it, and sometimes want to loose it. that’s just kind of my opinion (:

It's not acceptable. Just say you don't notice anything