Der Quatsch is a really common colloquial German word for nonsense. Or bollocks, if you’re very British.
- Du redest Quatsch.
- You’re talking nonsense.
- So einen Quatsch habe ich lange nicht mehr gehört.
- I’ve not hear such nonsense in a long time.
It’s not very strong and can even sound a little endearing depending on context.
And it’s very commonly used to express an idea of “Oh, don’t worry about it.”
- “Kannst du mein Bier bezahlen? Ich habe kein Geld dabei, ich geb dir das morgen zurück.”
“Ach Quatsch, ich lad’ dich ein.” - “Can you pay for my beer? I don’t have any money with me, I’ll pay you back tomorrow.”
“Ah, come on, nonsense, it’s on me.”
Oh and besides the noun, there’s also the verb quatschen and that’s a colloquial option for to chat.
- Ich habe Maria am Bahnhof getroffen und wir haben kurz gequatscht.
- I met Maria at the station and we chatted/talked for a bit.
The origin of these two words is likely an onomatopoeia, an imitation of a wet sound. How it moved to what it is today is not clear, but maybe, just maybe, it’s the sound of a facepalm.
By the way… if you need a strong option, for real, aggrevatingly nonsensical nonsense, der Schwachsinn is probably the better choice.