Even at the beginning of the scene Catherine Schell was laughing. Blake Edwards got frustrated because Schell couldn't keep it together and they had to do multiple takes.

Sellers can't keep it together. They never manage to. Edwards went with the best he could get.

                                   "Waiter, another cola and ginger ale, please."

 

                                       His "disguise" drooping mustache half off.

                                    Schell's shoulders are shaking she is laughing so hard inside. Still able to, mostly, hold it in.
 

 

        She knows what's going to happen next, he's going to fall over, but she still can't hold it in and giggles audibly. She is now beyond hope for the punch line no matter how many takes Edwards makes her do.

                                                   

                       She knows the punch line is coming but is too far gone as he prepares to deliver it.

                                              "Well, here's a-looking at you, kid."

                                                     It's contagious. Sellers begins to lose it.

                                        Schell inhales audibly--"Ahh!"in laughter, trying to stifle it so that she can sip her drink...

                           

                                      ...is "unsuccessful", further cracking Sellers up, takes a sip...

                                       ...and doubles over choking in laughter and cola and ginger ale.

                                        She really chokes!

 The entirety of the bar scene is 2:12. 

 

So, how was your afternoon?