I wasn't born yesterday

Feifei:	Hello and welcome to The English We Speak, I'm Feifei. And, as usual, I'm waiting for Neil, who's late. I think I'm going to get some revenge by playing a few jokes on him—especially as he forgot my birthday yesterday.
Neil:	Hi there, sorry, I'm late. Welcome to The English We Speak, I'm Neil and with me today is Feifei.
Feifei:	I've done all of that.
Neil:	OK, how are you, Feifei?
Feifei:	Not ... good ...
Neil:	Oh dear. What's the matter?
Feifei:	I can't believe you forgot.
Neil:	Forgot? Oh no, what have I forgotten?
Feifei:	What haven't you forgotten? Well, for a start, you were supposed to meet me an hour ago.
Neil:	Really? I thought I was only five minutes late.
Feifei:	An hour and five minutes late. Secondly, you were supposed to be dressed smartly as we are meeting that very famous guest later.
Neil:	Famous guest?
Feifei:	Yes, our very famous guest.
Neil:	Who's that, then?
Feifei:	How could you forget that Justin Bieber is coming in?!
Neil:	What!? My hero, Justin Bieber?! Where?! When?! Hang on a minute, Justin Bieber isn't coming in. I wasn't born yesterday, Feifei.
Feifei:	You weren't born yesterday but I was—well, twenty-something years ago. It was my birthday! And you forgot! In English, if you want to tell someone that they haven't made you believe an obvious lie, you can say I wasn't born yesterday. Here are some examples:

A: Did you know that I was the third man on the moon?
B: I wasn't born yesterday. You're British and I know that no British people have walked on the moon.

A: (Radio advert) Learn Russian in 3 days with just one minute's study an hour!
B: Those adverts are so stupid! The only way to learn a language is years of hard study and practice. I wasn't born yesterday.

Feifei:	So, you can say "I wasn't born yesterday" to show that you are not easily fooled.
Neil:	And I wasn't born yesterday, so I know that Feifei's claim it was her birthday yesterday isn't true.
Feifei:	No, that bit is true.
Neil:	Yeah, right. As I say: I wasn't born yesterday.
Feifei:	I was! I really was born yesterday. I had a party and everything. Where's my card and present?
Neil:	You're not going to fool me.
Feifei:	Argh, you're so annoying! I never forget your birthday, Neil.
Neil:	I know it wasn't your birthday yesterday ...
Feifei:	It was!