friends and girlfriends

How appropriate is it to tease friends about their friends of the opposite gender. I mean, when Y is meeting X often, but not that often, how do friends of Y determine if they are a couple or not ? My own take is in line with Mohnish Behl in Maine Pyar Kiya,

Ek jawaan laDka aur ek jawaan laDki kabhi sirf dost nahi ho sakte

I suspect this line is true, atleast when friend refers to someone you feel emotionally intimate with.

Refer to platonic, and advice by Carolyn Hax here, and here. This subject of course has been dealt with by experts: no solution has been found yet, and it is safe to say that none will ever be found. Anyway, in the meanwhile it is good fun for those not involved directlym and in a different way for those who are involved ;-)

ps: I remember reading an article about this "just friends" issue written by a guy in a college newspaper. This article became a sort of a cult classic, and got written about in the NYTimes/WaPo, but I can't find it by searching the web now.