Sorry about your friend
Without posting a very long out thread on the reasons why we (me and my family) laugh, I have to say that you summed it up.
When you're 12 and neither parent wants custody of you, so your grandfather takes you in - only to be confronted by your grandmother, who doesn't want to control her mental illness with medicine so you have to learn how to deal with her when she's not lucid; and then a little while later finding out that your little sister is really out to kill you because she is bipolar and cannot control herself so she becomes violent, chasing you with knives whenever she got the chance, overdosing three times - once taking her last breath in my arms on the way to the ER, having her run away time and again, etc. etc. etc.
Waking up each and every morning and praying for a "good" day, where I could actually try to live a normal teen-age life, was a daily prayer, and during my grandmother/sister's lucid moments, we laughed about their non-lucid moments. We made fun of them, they made fun of themselves. It was the way to get through it.
Instead of my DH's family using step-brother's condition and labeling him as disabled, his family made him do whatever every other kid in the family did on a daily basis. He had chores and he had to perform just like all the other kids in the family. He went to school every day and he had a pretty normal childhood for someone being mentally ********. Of course there were many many obstacles and they dealt with it, also with humor. To this day when we're sitting around talking, he will bring up all the naughty things he did while growing up and we laugh about it - him too.
In the opinion of many Americans, Political Correctness is Not Correct. Those who want it can have it. Those who don't want it shouldn't be forced to adhere to the wishes of the other side. That is our right as American Citizens. I choose not to.