Gender of Yordles
 

How come most guy yordles are fuzzy and all girl yordles have skin and no fur?

http://en.wikipedia.org/wiki/Sexual_dimorphism

But also because they used to be two seperate species, Meglings and Yordles, until they were retconned into one.

Megling genocide never forget.

Actually, only Tristana was a Megling
Anyway, Yordle males are sorta like other animals in that their fur coat and hue differ. This is to attract mates. Basically, the cutest ones gets the girls.
As for why Heimerdinger and Corki lack it, I believe it's because they shaved it to blend in a bit more with Piltover, or it may be a form of balding.

The "Meglings" aren't a species...

To why Corki and Heimerdinger look different, Yordles are supposed to change his appearance sightly depending on his/her enviroment, and are also affected by magic (Lulu has purple skin instead of blue ._.)

Chicks dig the fuzzy guys!

As I see it

Male Yordles are furry and can be of different colours, usually blue or something fair
Female Yordles are smooth skinned and always blue.

They used to be. Way back when, the Yordles and the Meglings were two different species, but Riot changed them to be one species to prevent confusion, but they kept the word Megling as a group of the Yordle military, of which Tristana is a member.

Also, I think Heimer and Corky are bald because they're older. They still have giant mustaches, though!

i think lulu is a megling, and she was just in that other world when the genocide happened, right?

i loveee teemoo