Bunkum is anything unacceptable, especially ridiculous lies. Calling something bunkum is like saying it's nonsense or rubbish.
There's a lot of BS in the world, and there's also a ton of words that mean something similar to BS or nonsense: like bunkum. People say "That's bunkum!" when something is false, crazy, or unfair. Getting fired for no reason is bunkum. A string of clichés from a politician is bunkum. An obvious lie is bunkum. This word especially applies to exaggerations and falsehoods. Someone who spins tall tales likes to talk bunkum, which is also called bunk.