My former sister-in-law got angry with me for laughing at the end of The Notebook once. I stand by my laughing. It was a stupid movie. I laugh at poor attempts at drama. If a show or movie does a sad scene right and they have a good build up to it, I won't laugh. Unfortunately most movies and shows these days aren't interested in good movie making, they want to entertain the lowest common denominator, get their money, and they will use all the proven cheap tricks to do so.
In RL, I still do it every now and then, but I keep it on the downlow by only laughing when other people laughing or by keeping it subtle by smiling and quietly chuckling.