If you happen to meet a child/person with autism...it's okay. They don't bite. Usually.
Sometimes their conversation is odd. Sometimes, they will talk about something endlessly. Sometimes they don't understand personal space.
But, guess what? They can be redirected very easily. Ask a question. Most can answer the question. Answer questions they may have. Most teens with autism have been taught how to have a conversation. They forget the rules sometimes, but can be sent back on track when they go "off topic". They know that term. They know to answer questions then to ask one right back. Why? How? Their therapists work very hard with them to teach them social skills.
By the time an child with autism has it teen years, they're aware of their differences. They just want to fit in. So, help them along. They know when you are lovingly helping them. Use humor.
What's not helpful? Answering a question with yes or no and then turning away effectively ending the conversation before it even starts. Rolling your eyes at them. Muttering under your breath to "Go home". Asking within hearing distance of a sibling "Why did you ask HIM?"
Above all? Remember the golden rule.