Having made a pact to not bring dates to their New Year's party, Monica decides to bring "Fun Bobby", Joey meets a pretty elf at the department store and invites her to the shindig, Rachel finds out that Paulo can make it to New York after all, Chandler breaks down (because of all the pressure of needing someone to kiss at midnight) and invites Janice, Phoebe is, of course, bringing her new love Scientist Guy (Hank Azario), and so Ross decides to bring his new roommate and pet, Marcel (a monkey) to the gathering.
Phoebe met Scientist Guy a few weeks back when she was playing guitar at Central Perk, and he and his friend were talking too loudly while she was trying to sing. The scene where she forces David (Scientist Guy)to tell everyone what he and his friend were talking about is hysterical, and the same can be said for the slow blossoming of their relationship. Indeed, the scene before their first kiss, where David says he feels he needs to sweep off the counter and then take Phoebe on top, but then he pauses before each item for different reasons ('well, this is just really expensive', 'this was a gift') and Phoebe blurts out that now he's basically just tidying up is a classic.(Much, much funnier than what I just wrote.)
In any case, the two of them fall in love and when the opportunity comes up for David to go to Minsk to research a special project, he decides (well, forces Phoebe to decide) to stay in NYC with her.
At the party, everyone's plans break down. Joey's cute date turns out to be a single mom who brought her two kids with her to the party, Janice mistakenly thinks that Chandler wants to restart a new relationship (as opposed to this one date - "kill me... seriously, kill me now"), "Fun Bobby's" grandfather passes away and since he can't get a flight out to his family, he comes to the party in tears, Paulo misses his flight and Rachel, while waiting at the airport, gets into a fight at the taxi stand that may have caused her to break a tooth, and Ross' monkey leaves his side the minute he walks into the apartment.
The saddest moment occurs, however, when it becomes clear to Phoebe just how much David truly wants this research opportunity and the two of them kiss and part before New Year's because "I don't want to start a New Year with you if I know I'm going to have to leave..."
Scientist Guy is an amazing character - this is true whenever we see him over the years - and it still amazes me that the writers thought that Phoebe would be better with Mike than with David. It is a joy to watch him act.