I try not to make fun of people who suffer from some bizarre and cruel disadvantage because I don't know what it is like to, say, have my family mauled by amok giraffes. If I make a joke about that unfortunate circumstance and someone says "My family was mauled by amok giraffes, you insensitive clod!" the humor is 1) that there is no misfortune so unlikely that someone hasnt' suffered from it and 2) that I really should have known that someone sho suffered such a fate was likely to see their personal trajedy made into a punch line.
I think what makes the invocation of this line from an actual sufferer of the malady when it wouldn't be OK otherwise is that the statement is both true and a punchline and therefore the joker presumably has some insight into the actual amount of hurtfulness that is going to be inflicted (I've given the matter less thought than the length of this post would indicate, so there are likely other reasons as well).
I'd hate to be that woman. In fiction it's Hitchcock but in real life it would be Kafka (unless she is guilty AND works in a cotton swab factory).
"Gotcha, you snot-necked weenies!" -- Post Bros. Comics