Generally accepted internet rule that states that there are no girls on the internet. Usually used with rule 34.
An actual real internets girl will typically NOT engage in explicit description of her sexual organs or their current, past, or projected future engagements. For example, a real Internet girl might mention she is on her period. This is fine, well within realgurl guidelines and a clear warning to leave the immediate vicinity. However, she is unlikely to describe the vile seepages involved. Eg: "The crimson ichor of my wymenhood cycle is leaking from my puffy, raw vagina (That aches to be fucked)."
'There are no girls on the internet' first gained popularity among what indisputably is the majority internet user demographic, the chronic unlayable.
A: Hey, I just spotted this hot chick!
B: Rule 16.