Anything with cancer really, it's generally not socially accepted.

Typhus, cholera and tuberculosis are all fine tho! Altho usually said as more of a slang version.

Oh, and wishing diseases upon someone is also a common thing. Altho again, when wishing cancer upon someone there's a very good chance you'll get into a fight.

Imo wishing cancer upon someone or a family member is the worst insult in Dutch.