Same here. I too laugh at inappropriate times and at things that ordinary people don't seem to think are funny. I've even been shamed for it which sometimes makes me want to laugh even more. I don't think that it is anything malicious or sadistic though. I think that different things strike different people different ways is a big part of it. When I was still a child and even a young adult and would hear of something bad happening to someone I would sometimes have an urge to smile even though I knew that what had happened was a sad thing. I even seen my mother do it just once. This lead to a lot of feelings of guilt for me feeling that way but, it hasn't happened to me in a very long time. I don't know if that's because I've learned to control it or what. But, "yes" I too laugh at pretty much anything that reminds me of slapstick comedy and I love the Three Stooges and 1940s-1950s era cartoon humor. I do think, like someone else mentioned that it may be tied in with anxiety or even nervousness or possibly even pent up laughter that just needs to come out. Maybe from frustration or something.