about "Witness" in this passage
"No, I'm telling you last night was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness."

Question1: what does witness mean? does it refer to a film or something like a book?

Question2: can i make up a sentence like "No, I'm telling you yesterday was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness." to express my happiness?

the whole passage comes from Friends:

Paul: Thank you! Thank you so much!

Monica: Stop!

Paul: No, I'm telling you last night was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness.

Monica: We'll talk later.

Question

about "Witness" in this passage 
"No, I'm telling you last night was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness."

Question1: what does witness mean? does it refer to a film or something like a book?

Question2: can i make up a sentence like "No, I'm telling you yesterday was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness." to express my happiness?

the whole passage comes from Friends:

Paul: Thank you! Thank you so much!

Monica: Stop!

Paul: No, I'm telling you last night was like umm, all my birthdays, both graduations, plus the barn raising scene in Witness.

Monica: We'll talk later.

Answer

The word "Witness" here is a title of a movie from 1985 staring Harrison Ford. A "barn raising" was an act performed by members of a small community where everyone helps a local family build a barn.

http://en.wikipedia.org/wiki/Witness_(1985_movie)

Cheers!

Answer

Question 1: Witness refers to a book or film.

Question 2: You could use a similar construction, however unless you've had two graduations you wouldn't say that, also people from our generation probably won't have seen Witness (I know I haven't) so they wouldn't get the reference. It is not a set phrase. But, a similar semi-set phrase is "It (referring to a specific event) was like all my birthdays and Christmases rolled into one!" - meaning that it was a really amazing experience/day.

hope that helps!