Maybe I should just let this go, but I'm finding that difficult. A co-worker made what he considered to be a joking statement about people with a certain disease. I contradicted the statement, but he re-iterated what he'd said more forcefully. It wasn't really offensive in any usual way, but just stupid and insensitive and inconsiderate. Given that I lost a parent and several other family members to different types of this disease, it brings up painful memories also.
Also, the boss was sitting right there the whole time. Unfortunately, the co-worker seems to be the boss' favorite (he is very knowledgeable and productive, so his social shortcomings seem to be ignored).
Edit to clarify a few things: This person does frequently say things that are, in my opinion at least, inappropriate. Sometimes it's insensitive humor like this, sometimes it's over use of foul language, sometimes it's just insults (usually directed at someone outside our group). Also, as I stated in a comment, the situation is complicated with several contractors working on a long term project for a large organization and we work for different companies; escalating this to his company's HR department would be difficult.