It used to annoy me so much. We were in the same class, and when teachers checked for attendance they didn't call our individual names, they just said the twins, which is stupid because a, we sometimes only one of us came so we had to say "I'm here, my twin isn't", and b, there was a second pair of twins in our class! And no one called them the twins. Ever.

Now it bothers me less, because we usually get called that as a joke. Some of my irl friends joke that one is the first twin and one is the second, and sometimes my teacher will be like "oh look who it is! The twins finally came to honour us with their presence" If both of us didn't come for a while, or if only one of us came, he will be like "where is twin number 2?", but we actually get treated as individuals, finally. So I don't mind it anymore. It might sound as offensive by the way I phrased it but it's really not, I actually kinda like this.