It depends on the context. I don't use it to be insulting, but it could be. There's a difference between "you're too skinny," or "oh you're so skinny" or "I wish I were skinny like you." Just take care of yourself and don't worry about other people running their mouths.
My ED takes being called skinny (as in, too skinny) as a compliment. My rational brain knows it's unhealthy.
ETA- I'm not insinuating that you have an ED though. I never assume that someone else has an ED just because they're underweight.
Considering that you have a BMI of ~15, I would NOT consider "skinny" a complement.
You mentioned it in another thread...
I'd take it as a compliment if I was a healthy weight. If I was underweight, I'd feel insulted.
It also depends on context. Even at a healthy weight, the word skinny can be used negatively.
At a BMI of 15, you're closer to death than you are to living. :( I'm glad you are trying to rectify the situation. Be sure to keep in contact with a doctor.
if someone calls you skinny and tells you it's a compliment they are furthering your body image issues. You are not at a healthy weight.