Still... you didn't say Type 2 diabetes, you just said Diabetes.
Sounds like you are making fun of all people with diabetes.
And the things is, most people are completely ignorant that there is any difference.
So many people tells my boyfriend
"But you're not fat, you're healthy! How do you have diabetes?"
There is so much stigma around a disease that fucking kills people horribly. They go blind. They lose their feet, hands and fingers.
If you are the type of cruel person that feels that they deserve more punishment for their life choices, (and be honest, we all make poor life choices), then accept that their diabetes alone is their punishment. There is no need to mock them.
I wouldn't make fun of people with cancer just because some people get lung cancer from smoking.