Step 1 : Introduction to the question "1. My friend and I were playing basketball in the park when he stopped me and pointed. I looked in the direction, and he was pointing to a girl. He said "she's so fly" and we started playing again. I had no idea what that meant. Perhaps you know?"
...1. He thought she was his cousin 2. He thought she was ugly 3. He thought she was attractive 4. He thought she was old Fly before 2000: What a bird or a plane or Superman does, or an annoying insect, also slang for cool (It was used in "In Living Color" in the 90s [thanks ferfer72]) Fly after 2000: Attractive, pretty, cool I remember saying "good-looking" or "hot" when someone was pretty. But my friend, he said she was "fly". It seems that the English language has been morphed into a completely new language, which I will call "teenspeak".