I came up with this joke late at night...don't judge

Imagine you've just moved to a new high school. You meet a friend who's been home schooled her whole life. During a conversation to get to know her, she tells you that her parents never gave her the talk . She's pretty skinny but as the year goes on you notice that she gains some weight. Of course you don't want to upset her, so you stay quiet. By the last month of school the teacher begins Sex Ed. After the first lesson,about safe sex is over, you talk to your friend.

She giggles and whispers to you:

"Well, that lesson was nine months late"

If you don't get it, comment and I'll explain it ;)