For those of you that never saw it, here is the gist I believe. I saw the punchline but just the idea of exactly how it started...correct me if I am wrong:
When Ross and Rachel are planning to settle down, the subject of never being with another person for the rest of their lives.
So they agree to each have a "shag list" of 5 people who if the opportunity arose, they could shag with it being "unfaithful" to the other person.
They both have film stars and the like so it is not something that is likely to happen, the punchline being the biggest star on Rachel's list walking into the coffee shop and then chatting her up...forget who it was.
Me and Rach found it amusing so did the same. Hers were:
1. Colin Firth
2. Hugh Jackman
3. Niall Quinn
4. Tommy Lee Jones (

? this one must show what she sees in me)
5. I forget
It's a bit of fun, nothing sordid.
Also you are not allowed to include easily available people, which is why my last list was a joke.
My real list was:
1. Halle Berry
2. Daisy Donovan
3. Ronni Ancona
4. Vicky Coren (pre super rich too)
5. The black girl from that womens football show (forget her name)
2&3 Pretty and funny...always a winner. Actually that goes for 4 too.