Idioms with 'y'

a yes-man: someone who tries to get approval by agreeing with everyone.
A: "Why does the boss think Arnold is so intelligent?"
B: "Because Arnold is a yes-man. He agrees with everything the boss says!"

You don't say!: Really? / Is that really true?
A: "Have you heard the news? Jessica got married!"
B: "You don't say!"

You've got to be kidding!: You can't be serious! (What you said can't be true. What you said is very surprising/hard to believe.) "
A: "Did you know that Bob quit his job?"
B: "You've got to be kidding!"

Yucky: terrible; distasteful; very unpleasant.
"Don't eat the soup at the cafeteria. It's yucky!"

Yummy: delicious.
"Have you tried the cookies that Jonathan baked? They're yummy!"