Due to the unplanned appearance of Billy Crystal and Robin Williams, their conversation in the coffee shop is completely improvised, including Joey's interruption.
Billy Crystal and Robin Williams's appearance wasn't in the original script. They were, by coincidence, in the same building, or the one across the street from where "Friends" was being filmed, and the writers asked if they wanted to make a guest appearance. This was the day of shooting so it was just quickly thrown in.
Pete says his trainer Hoshi is a former assassin and quickly corrects that to say house painter. "House painting" is indeed a term used in organized crime as code for a hit job.
Robin Williams and Billy Crystal's cameo in the opening scene coincided with the release of their film, Fathers' Day (1997), which opened the day after this episode aired.
Monica was supposed to have a line after the two men played by Robin Williams and Billy Crystal left but Courteney Cox was so flummoxed that she genuinely forgot what she was supposed to say so ad libbed that she forgot what she wanted to tell them.