___ cheese (cheese that isn’t yours, in a classic joke) Crossword Clue

 The answer to the crossword clue "____ cheese (cheese that isn’t yours, in a classic joke)" is NACHO.

The joke is: "What do you call cheese that isn't yours? Nacho cheese!"

Nacho cheese is a type of melted cheese that is often served with nachos. It is typically made with cheddar cheese, but other cheeses can also be used.

The joke is funny because it plays on the fact that the word "nacho" sounds like the word "no". The implication is that if you take someone else's cheese, they are going to say "no".

I hope this helps!