der Käse
cheese
A solid or semi-solid food made by curdling milk.
Zum Frühstück esse ich am liebsten Brot mit Käse.
For breakfast, I like eating bread with cheese best.

cheese / nonsense
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cheese
A solid or semi-solid food made by curdling milk.
Zum Frühstück esse ich am liebsten Brot mit Käse.
For breakfast, I like eating bread with cheese best.

The meaning of 'Unsinn' (nonsense) or 'Blödsinn' (rubbish) for 'Käse' (cheese / nonsense) is purely colloquial. It is used to dismiss a statement as stupid, wrong, or irrelevant.
Glaub ihm nicht, er redet nur Käse.
Don't believe him; he's just talking nonsense.
In the colloquial meaning, 'Käse' (cheese / nonsense) appears in fixed expressions. You often hear 'So ein Käse!' (What nonsense!) as an exclamation or the request 'Erzähl doch keinen Käse!' (Don't talk nonsense!). The verb is often 'sein' (to be) or 'erzählen' (to tell).
Seine Ausrede ist doch totaler Käse.
His excuse is total nonsense.
Whether the food or 'Unsinn' (nonsense) is meant is revealed by the context. If it's about eating, cooking, or shopping, it means the food. If it's about opinions, stories, or explanations, it often means 'Unsinn' (nonsense).
Für die Pizza brauche ich noch geriebenen Käse.
I still need grated cheese for the pizza.
crap / manure
'der Mist' and 'der Käse' can both be used colloquially to express that something is nonsense, bad, or annoying. 'Mist' often sounds stronger and more emotional. It is also used as an exclamation when something goes wrong. 'Käse' usually sounds a bit lighter and often means that an idea, statement, or thing is nonsensical. Both words are more suitable for casual conversations, not formal situations.

Was er über den neuen Plan erzählt, ist doch völliger Käse.
What he's saying about the new plan is complete nonsense.
So ein Mist, der Zug ist gerade ohne uns abgefahren.
Damn, the train just left without us.