If you're laughing, snorting, chuckling, giggling, or smiling darkly into your beard, it is probably humour (Amer. humor) that has set you off.
Humour is the art of being funny. It comes in many shapes and sizes, from fat men slipping on banana skins to dark jokes about the economy to simple line-drawings about cows and ducks called Elmer and Jedd.
A humour is also a bodily fluid, or a mood. Or alternatively you can 'humour' someone by letting them have their way.
Often, we in the PPC refuse to humour Sues and Sue-wraiths, instead spilling their vital humours and laughing at the dark humour of it all. This puts them in a very bad humour. Or it would, if they weren't dead.
The above sentence was not, in itself, particularly funny, but we're willing to bet most PPC agents would crack a smile at it. This is an example of workplace humour.