Explanations

GONNA= (coll.) Going to.

RETURN IT= If you buy something or somebody buys something for you and you return it, you take it back to the shop because you don’t like it and you want to change it for something different or have a refund (get your money back).

NOT THIS SECOND= Not right now, not at this very moment (but maybe later).

YOU GUYS (coll. AmE)= A very common way to distinguish between the 2nd singular form (you) and the 2nd plural form (you guys) for both the masculine and the feminine or mixed.

WENDY IS A FAT GIRL NAME= She’s jealous of this Wendy who is with her husband at work. She doesn’t know her but she thinks that name sounds like she must be fat.

AREN’T WE DONE WITH THAT?= Haven’t we finished with that?, didn’t we stop talking about it?. If you are done with something you have finished it or you stop thinking about it. If you are done, you have finished. Are you done? = have you finished?

A COPYING MACHINE= A machine to make photocopies (also called "a copier machine" or simply "a copier"). Pronunciation of "machine": /məʃi:n/.

I MISSED YOU= If you miss somebody you are not with them but you want to be with them.

WHO DID YOU MISS THE MOST?= Pay attention to this superlative form. To make the superlative form of the verb we put "the most" after the verb. (e.g. "I love you the most" = I love you more than I love anybody else; I don’t love anybody more than you).

YA(coll.)= You.

GOT YA!= I knew you would do/say/think that.

TO GET FIRED= If you get fired you lose your job because your employer dismisses you, kicks you out.

TURNS OUT= The surprising fact is that...

QUIT= Sop doing something. If you quit your job, you leave it voluntarily.

THINK SOMETHING THROUGH= Ponder; think carefully about something.

WANNA(coll.)= Want to.

YOUR BEING HERE IS...= When the verb is the subject of a sentence, it usually goes in the -ing form:
- Dancing makes me happy (I love dancing)
If this –ing form has its own subject, then we can use the pronoun or the possessive:
- You dancing makes me happy.
- Your dancing makes me happy.
So the sentence "your being here is the best Xmas present" means "You are here, that’s the best Xmas present".

GIFT= present.

PASS THESE, WILL YA? = Will you pass these? (do you want to pass theses?). When asking for a favour, it is common in colloquial English to remove the WILL and the subject and put them at the end, as in a question tag:
- Will you help me with this? = Help me with this, will you?

A DONATION= Something (usually money) that you give to a person or organization that needs it, usually for charity or to support them.

HOW DID YOU KNOW?= This is an expression of surprise. When they give you a present and you like it very much (or you pretend you liked it very much), you say "How did you know?", which means "how did you know this is exactly what I wanted?". In this conversation, though, Ross is ironic, he doesn’t like his present at all, the intonation makes it clear (he shows disappointment, not surprise).

ARE YOU KIDDING= Are you joking? Is this a joke?

TIMELY= If something happens timely or is timely, it happens at the right time.

A TIMELY START TO THINKING ABOUT OTHER PEOPLE= The right time to start thinking about others. In this conversation they say "a start to thinking about...", so START here is not a verb, it’s a noun, and TO is not the mark of infinite, but a preposition, and after prepositions and conjunctions, we use the –ING form of the verb.

BESIDES= In addition to that,

THIS GIFT STILL SAYS I LOVE YOU GUYS= Even if you don’t like it, this present is a symbol of my love for you all.

LILIAN MYERS= She was a political candidate raising money for the elections. Chandler made a donation for her in the name of Joey.

ACTUARY= A statistician who computes insurance risks and premiums.

TOPLESS DANCER= A girl who dances in bare chest (wearing nothing on her chest).

D’YOU= /dʒu:/ Do you. In normal conversation, quite often DO loses its vowel, especially before YOU. When D and Y get into contact, most of the times we pronounce a sound like in the beginning of "John", so "d’you" usually is pronounced like "Jew" ("joo").

REALIZE= If you realize something you understand it correctly.

SOLE= Only.

WAGE EARNER= A person who earns money (a wage is a weekly salary).

THE HOUSEHOLD= The family as an economic unit.

A KEPT MAN= A kept person is somebody who doesn’t work but gets money from their husband/wife/lover.

BUCKS (coll. AmE)= dollars.

GO BUY YOURSELF= Go and buy something for you = go to buy...
GO is followed by infinitive with to, but very often we use it followed by AND:
- I’ll go to make some tea = I’ll go and make some tea.
In AmE, they often drop AND in colloquial conversation, so they’d say:
- I’ll go make some tea.