Arsthbt

I started watching this film late at night a few years ago. UK.
I suddenly leaped up and grabbed the remote and switched it off.

This woman was setting off to have sex with a bloke and the viewpoint switched to inside her, there was snarling noises and rows of teeth in her vagina waiting to bite him.

I found it disturbing and went to bed (nerves jangled all night!).

This is probably Teeth (2007). Not a good film, but it does match your description.

From IMDB:

Still a stranger to her own body, a high school student discovers she has a physical advantage when she becomes the object of male violence.

This trope has a TvTropes page named Vagina Dentata, which translates by itself. And it cites the "most obvious example of all" to be Teeth (2007).

Dawn grows up in the shadow of a nuclear power plant. In high school, while her biology class studies evolution, she realizes she may have a hidden curse, an "adaptation." She lives with her mom, step-father, and hard-edged step-brother. She likes Tobey, a guy at school, and he likes her. She takes a pledge to remain chaste until marriage, so they date in groups, watch G-rated films, and don't kiss, but the power of teen hormones is great, so temptation beckons. Dawn has an admirer in Ryan, and when when things have an unexpected twist with Tobey, she turns to Ryan for help. Will he be her mythical hero and rescue her? Or can she find her way as her own hero, turning the curse into an asset?

The trailer is not that unsafe for work, but I'm guessing the movie might be...

Sounds like the 2007 horror comedy Teeth

Dawn (Jess Weixler) is an active member of her high-school chastity club but, when she meets Tobey (Hale Appleman), nature takes its course, and the pair answer the call. They suddenly learn she is a living example of the vagina dentata myth, when the encounter takes a grisly turn.