Even though I didn't find it funny, I used to smile when I told people bad news. I remember the first time I noticed it, when I told one friend of mine that another friend of ours was dead. I remember feeling my face in a big smile. I asked her "Am I really smiling? I'm not happy, I'm sad and I don't know why I'm smiling when I'm talking about this". She told me then that I always do that. I've tried to notice it and not do it since then.
Finding things funny that are horrible is another thing. Sometimes I'll hear a story that can just be horrible but it sounds funny because of the way it's told or the fact that if it were on tv in a sitcom or something it would be funny. Mainly because then it wouldn't be real. Like that story about the guy shooting the cats as a misunderstanding. Happened to a guy my husband worked with and his wife kicked him out over it. He wasn't the one who shot the cats, he told his stupid redneck brother to get rid of the cats while he took his wife out to dinner and all for the evening. While he was gone the brother comes over with a .22 and picks the cats off and leaves them where he shot them. The guy meant "take them to a shelter, preferably a no kill shelter while we are gone" but the redneck brother took get rid of the cats to be a Soprano type expression, and did. The guys wife kicked him out after that. They are back together and all but it was a funny story, especially when told in true Southern style. However, the reality of it is terrible, and not funny.
Although that guy who combined RC helicopters and taxidermy on his dead cat is still kind of funny, even after I've seen the videos.