My answer is ... I'm really not sure!
There's only 1 'possible' ... long time ago, high school sweetheart, me 18, her 17. She was a good girl, and really fit! Dated her for about 3 months before 'the time was right' (time was right after the first date as far as I was concerned!
Anyway, when it finally happened she bled. - and it wasn't a period as she was on the pill for medical reasons (to regulate and lessen the pain of extremely painful periods). After 3 months dating this gorgeous, sexy thing I was, let's say ... very enthusiastic! Now she had previously told me she wasn't a virgin. So I was very surprised to see blood! When I pointed out she had told me she'd had sex with 1 guy before she said "yes, but not like that!"
I never did pluck up the courage to ask her exactly what she meant! I can think of loads of possible explanations now ...