Here is the way I deal with gender online:
First, ignore any real life connections between a user and an owner and address them by whichever pronoun they prefer. If they tell me they are a girl, I be polite and say she.
Second, if they indicated no gender, attempt to judge by their name. This doesn't always work, but people who name themselves anglekittenrainbowsunflower generally don't mind being addressed by the pronoun she.
Third, assume masculinity if no preferred gender is indicated and there are no other clues. It has nothing to do with "no girls on the Internet," it's an English standard.
Whoever doesn't get the four: Count to 4 in binary on your fingers.
Hold your hands in front of you, palms toward you. Extend your fingers. Beginning with your left index finger, assign each finger a digit beginning with 1 and ending with 8. Close your hand. When a finger is extended, that place is considered to be a 1. When your finger is at rest, or lying down, that is considered to be 0. By raising and lowering your fingers in different patterns, you can count any positive integer between 0 and 255. Thumbs are ignored.
Here is how to count from 1 to 4 in binary using this system.
1. Raise your right index finger.
2. Lower your right index finger. Raise your right middle finger.
3. Raise your right index finger.
4. Lower right index finger and your right middle finger. Raise your right ring finger.
Congratulations.
