So you think you're funny when you wear a big red nose? Others might think differently, according to this German word.
A Pappnase (literally, a cardboard nose) is usually made of red plastic and it's supposed to be funny. It's what lazy people put on for carnival when they can't be bothered to get dressed up properly.
Just because you're wearing a Pappnase, you think you look as if you're obviously really into Carnival. But real Carnivalists spend huge amounts of money and/or time on their costumes, and you just can't be bothered. Actually, you look like a bit of an idiot - which is fine, since that's the other meaning of Pappnase. If you just wear a Pappnase for Carnival, you must be a Pappnase!