What Defines Something as Funny?

I notice that every person has their own definitions of what someone defines as funny. What I found funny was how Allison Bechdel in the novel Fun Home,  found it funny that her father had passed.
On page 227, Bechdel brings up an interesting point. She writes, "They say grief takes many forms, including the absence of grief." On this page shows specific pictures of Bechdel at her summer job in the library, explaining to a co-worker about her father's passing. Because she is laughing, he does not believe her. She then asks him, "Why don't you believe me?" He then responds with, "Because you are laughing." As she further explains how her father died, she then goes into hysterics (laughing.) She then writes, "The idea that my vital, passionate father was decomposing in a grave was ridiculous."
It is here in that statement Bechdel shows somewhat a warmth for her father, saying how he was passionate, especially about literature and the English language. To her, it seems ridiculous the father she knew and somewhat loved was gone. Perhaps she was in denial and that is why she laughed. I realize everyone has their own ways of coping with death, myself included. I also laugh at death which masks my fear of it. Maybe Bechdel was in denial, like mentioned before, or was masking a fear of not having someone close to her as a family member who has a need to be accepted and masks their true self (sexuality.)
I think despite the troubles that Allison Bechdel had with her father they were similar in the sense that they hid their true selves. For example, they have a moment of truth and connecting when they are in the car on their way to the movies on page 221 and he admits to wanting to dress like a girl and she admits to wanting to be a boy! It is in this moment their secrets of their sexual orientation come out and they can admit who they are. This shows the remembrance and affection for her father. Especially so on the last page, when ironically enough she looks back on her father on page 232, and says "He was there to catch me when I leapt." All in all, maybe she could not believe he was gone, and defined her father's death as funny. But she'll always remember the unspoken bond they had.