ITT stands for "In This Thread". It generally precedes an ironic reiteration of something funny/incorrect that has appeared in the thread. Example: Saying "ITT: All Galkas are dumb" would be akin to making fun of someone else in the thread who intimated that all Galkas were dumb.

So no, I'm fairly sure Gokku knows that there are females on the internet. Most people do. It's simply never a good idea to take someone's personal information at face value over the internet, because anyone could really be anyone. It is simply safer to assume that everyone online should be treated as if they were a fellow male. If anything, most females I know appreciate this because it means they aren't getting stupid amounts of unwanted attention or being hit on by 14 year olds with an IQ lower than potato. Anonymity is the ultimate equalizer of the sexes.