What is black humor? Well the wikipedia definition is a good one: a sub-genre of comedy and satire in which topics and events that are usually regarded as taboo are treated in a satirical or humorous manner while retaining their seriousness. Synonyms include dark comedy, black comedy, dark humor, and morbid humor.

This image of how not to fast-rope onto a ship is an excellent example of that:

The recent events of the Israeli Defence Forces trying to stop the flotilla trying to break the embargo of Gaza is a deadly serious matter and it hardly seems worthy of laughter. However, this pseudo-instructional image satirizes and mocks the IDF for doing what they obviously should not have done. (At least in the eyes of the illustrator). I am a big fan of black humor: it is sometimes the only way to deal with extermely difficult subjects. This is a well done example of it.

From Fast-Roping 101 – The Daily Dish  By Andrew Sullivan