Is AUTHOR wrong in the post ? POST : Background: I work at an organization that focuses a majority of their efforts in caring for people that have mental health issues. 

Situation: There were 7 coworkers left at a long time coworkers going away party. 3 of which are part of the administrative team, 2 supervisors, a fairly new employee, and me. During one of the conversations we were having a coworker, who is always cracking jokes and is part of the supervisor team, starts reminiscing on funny stories of the employee, who is going away. One of the stories he told included a part about his sister, who was held back in grade school because she was too shy. 
After the story, a coworker, who is not part of the administrative team and fairly new, says out loud, “I was almost held back from kindergarten because they thought I was autistic.” There was a short pause and then the coworker, who was telling funny stories said, “and the verdict is still out!” At this point, the coworker who said it, started to laugh, and I also started to die laughing. I was laughing so hard because the poor girl had left herself open for a joke like that and for him cracking a joke about her possibly being autistic at a mental health organization. Everyone laughed, but realized that the joke was inappropriate, and settled down. I continued to laugh to the point were I began to tear up. After my good hard laugh, the coworker, who was made fun of says to me seriously, “why are you laughing.” To which I respond, “because it was funny.” 
I composed myself and hung out until everyone cleared the room and had the chance to talk to the leaving coworker. 

When I repeated this story to my girlfriend, she told me that I was the asshole for laughing, which is something that had not crossed my mind because I was not the one who told the joke. 

So who is the asshole? The guy who made the joke or me for laughing at the joke so hard? 
