What does"Vinyl" mean in Friends S01E13?
Phoebe : Isn't he great?

Rachel : He's so cute! And he seems to like you so much.

Phoebe : I know, I know. So sweet... and so complicated. And for a shrink, he's not too shrinky, y'know?

Monica : So, you think you'll do it on his couch?

Phoebe : Oh, I don't know, I don't know. I think that's a little weird, y'know? Vinyl.

Question

What does"Vinyl" mean in Friends S01E13?
Phoebe : Isn't he great?

Rachel : He's so cute! And he seems to like you so much.

Phoebe : I know, I know. So sweet... and so complicated. And for a shrink, he's not too shrinky, y'know?

Monica : So, you think you'll do it on his couch?

Phoebe : Oh, I don't know, I don't know. I think that's a little weird, y'know? Vinyl.

Answer

Vinyl is a fake leather.

The joke is, she would do it on the couch with many materials.. but maybe not that one.

Jessie, try Seinfeld.  I would much rather answer Seinfeld questions! hehe.

Answer

It means that  unlike soft leather, a  hard vinyl couch would be a very uncomfortable place to have sex.

Answer

It's a synthetic material, so what it means would depend on the context--it could be furniture, flooring material, LP records, almost anything.
http://en.wikipedia.org/wiki/Vinyl_%28disambiguation%29

Here, she is referring to the fact that the couch is surfaced with vinyl. I'm not sure why she thinks it is weird, maybe just because vinyl is a slippery,cold material, but also more likely because vinyl clothes are associated with "fetish" sexual lifestyles (kink, BDSM, call it what you will) in western culture, maybe the association of the material with sex is too "weird" for her!