No Girls on the Internet
A common meme, No Girls on the Internet means exactly what it says. The phrase originates from the godawful Early Days of the Internet, where it was seen as the dominion of basement-dwelling, generally male nerds. Most of these have since migrated to /tg/, so the meme fits perfectly.
A /b/tard said this:
If I can pontificate a bit, for your edification. One of the rules of the Internet is: "there are no girls on the Internet." This rule does not mean what you think it means. In real life, people like you merely for being a girl. They want to fuck you, so they pay attention to you and they pretend what you have to say is interesting, whether or not you are genuinely interesting, or that you are smart of clever, whether or not you are actually smart or clever. On the Internet, there is no chance to fuck you; this means the advantage of being a "girl" does not exist. You don't get a bonus to conversation just because someone wants to put their cock in you.
When you make a post like "hurr durr, I'm a gurl," you are begging for attention. The only reason to post it is because you want your girl-advantage back, because you are too vapid or too stupid to do or say anything interesting without it. You are forgetting the rule "there are no girls on the Internet." The one way around this rule, the one way you can get your "girlness" back on the Internet, is to post your tits. This is, and should be, degrading for you, an admission that the only interesting thing about you is your naked body.
In short: TITS OR GET THE FUCK OUT
 The Hard Truth of the Matter
Even though it has changed in recent years with more female tabletop gamers (and more female interest in sci-fi and fantasy in general), Have you ever wondered why you don't see more girls involved in tabletop gaming? It is exactly this mentality. Turns out people in general (be they Black, White, Asian, Gay, Straight, Male, Female and so forth) don't like being subject to causal bigotry, and no, claiming that it is "Joking" AT MOST glosses over about 0.5% of such activity, and yes straight men can and do interact with known women without even considering attempting to get them in the sack.
No, this is not some crazy feminist extremist message, it is called common fucking courtesy. If the tables were turned, you would likely be driven away as well. And in the end you only suffer from this. Imagine all those people that happen to be female who, if they got into it could come up with interesting and inventive homebrew settings, well constructed characters and campaigns, or even are not goddesses of creation someone who contributes their share to the experience in a positive manner, but never do because a bunch of unenlightened basement dwelling Troglodytes drive them away with a barrage of stupid insults that lost any theoretical comedy value they might have had over a decade ago.
Someone with common sense and social understanding.
It is generally safe to assume that someone is male until proven otherwise.