OP was an asshole for how he reacted. She was looking at vibrators. She didn't ask to buy one. She wasn't doing anything wrong. He flipped out and slammed her computer shut and grounded her for a month.  

Imagine the stigma he created about her sexuality. What damage did he just do? When she's older and she is having sex, what if something goes wrong? She will no longer trust her dad when she needs help. Example: instead of asking for birth control when she's older, she may be ashamed or scared to ask him to bring her to a doctor. She will still have sex. Now she's knocked up. That's a much bigger issue to deal with.   

He should have turned around and left before she noticed him watching over her should and had a short sex ed talk, calmly, later.  

The issue of buying or not buying a vibrator is irrelevant I think, she wasnt asking him to in the first place.