How to accept an apology gracefully

One of my favourite classes is my advanced intermediate class on Saturdays.
Today's lesson on 'apologising':

N: I'm afraid I lost an important document. I can't apologise enough.
S: What?! You're fired!!
N: What?! Oh, no!... really? :(
S: Hahaha! Just kidding!
N: Oh, thank goodness. I'm really sorry about this.
S: Which file was it?
N: It was the document with all the sensitive customer information.
S: Oh. You're really fired!

S: I'm sorry, I lost my security key card.
N: Oh, really? Where did you lose it?
S: I think it's in a taxi. I was really drunk last night...

S (bowing): I'm sorry I stole your wallet.
N: What?! You... you stole my wallet?
S: You shouldn't have left it on the table.
N: But... I... If you give it back, I guess it's okay.
S (bowing again): I have a very old father... and a very old mother...

A: I have to apologise for kissing your girlfriend.
S: Oh. Which one? I have several girlfriends.
A: The one at this school.
S: Yes, I have several at this school, some at work...
A: Oh. It's Namie.
S: Oh, that's okay. She's not an important girlfriend anyway.
A: Oh, thank you. I'll make it up to you. You can kiss my girlfriend.