how elusive is "it"

"I used to be with "it", but then they changed what "it" was...now what I'm with isn't "it", and what's "it" seems weird and scary to me"
- Abe Simpson

Who decides who or what is the "it thing"? Who dubs the "it girl" or "it guy"? the "it restaurant" or "it club" or "it artist"?

I'd really like to know these emminent "it makers", the "gods of cool" so to speak - I have a few "it" things I'd like to propose....

a) day-of-the-week socks, displayed proudly over one's leggings (what better way to show how "with it" you are than overtly exibiting your knowledge of the weekdays?)
b) blue nail polish (has blue nailpolish already had its 15 minutes? what if i said it had to be the exact shade that would constantly make you look slightly frostbitten - perfect for canada as you probably are slightly frostbitten, lets turn it into a fashion statement)
c) DEEP FRIED CARBS (and, accordingly...
d) figure-masking shifts or frocks (whichever you prefer) - actually, i guess these ARE in right now, so lets make C happen and we can all live like kings