I think there are 2 problems here:
1. What do you mean by "cute"? This can have several meanings. In British English:
(a) beautiful, small and sweet, to describe a baby or a kitten
(b) attractive, to describe a girl (say 15-30 years old) (but be careful, if she did not want this attention)
(c) sharp, cutting, "too clever", rude and offensive (e.g. "don't get cute with me!")
However in the US, (I think) "cute" is a much more general term to mean attractive. I've seen people call my 60-year old mother cute (and being British, she was horrified and even offended).
So, are you trying to me funny or offensive?
2) However you say it, I would simply find your comments extremely old-fashioned and unnecessary. The trend today is not to fat-shame (celebrities are also calling this out on the internet - just google "fat shaming"). And we are also now more mindful of mental health issues. So think carefully before you say something nasty, to be really sure of the effect you will have on that person, no matter if you meant it as a joke.