Student or Learner
Is this "You canít be serious." commonly used instead of "Don't be kidding"?
M: Jane, you know what? Iíve won the first
prize in the lottery.
W: You canít be serious.
M: Yes, I am. I canít wait till the money
comes in tomorrow.
W: You are the lottery winner
"You're kidding" is the common phrase. Some alternatives:
You're having me on.
You're having a laugh.
You're having a giraffe. (A type of rhyming slang)
Are you kidding?
Are you kidding me?
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Also, "Pull the other one" ('one' referring to 'leg').
As 5jj said, I learned "Are you pulling my legs?" is a common expression. Isn't it?
NOT A TEACHER
To my knowledge, people usually say "leg", not "legs". See also here pull leg - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.
One more for the list: No way!
(Yes, it's the single "leg." You're pulling my leg.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.