Why is it sometimes deemed offensive to call women "females"?

[Abstamyous]

I'd rather all the people who refer to me as "girl" call me female.

 

[user 148069]

I hear a ferengi voice in this question

but back on topic, I'm not sure since I'm not really bothered by it. Strangely enough most folks online think I'm a dude.
maybe referring to ladies as "she" rather than female would be less offensive? I don't know...