Sometimes you simply can't help it, and you break into uncontrollable laughter at the least appropriate time possible. It makes sense, when you think about it, since laughter often comes as a reflexive response to discomfort and absurdity.
Even so, it's hard to explain that it's reflexive and not personal when you start losing your breath laughing at a funeral, or at someone else's unfortunate story.
In a popular Reddit thread, people shared stories of the worst time they lost it laughing, and it will make you feel infinitely better about your own memories of insensitive giggling.
This was at a ballet school performance. It was for kids ranging from 5 to 16 year olds.
For one of the younger age groups they did this thing where one kid pranced from one corner of the stage to the other, and then another kid would do the opposite, in a big X pattern. And they would have these gigantic sh*t-eating grins on their faces. Just horribly precious.