Personally, I think it is rude that her partner laughed at her when she attempted to dirty talk. That is the best way for her to lose all motivation to try it again!

I think the guy has to be a little more sensitive to his partners discomfort. I think that the reader should attempt to dirty talk, following her partners queues but instead of having her partner making her feel insecure, he should encourage her to try different dirty words and tell her which he prefers.

If he does laugh it should be about the situation and not her, that way it will decrease the tension and she could laugh as well.

Perhaps planning a role play would help with the dirty talk. Sometimes playing a character allows you to be more adventurous as the dirty talking is coming from the character being played. You might want to chose a character that fits with the relationship/dirty talk.

For example, if he is more dominant and likes to call you a dirty girl, you could dress up as a school girl, a maid or just a submissive type of character. If he likes to have you in control, you could play the police officer, the business woman, or any other character that makes you feel dominant! The dirty talk will fit with the character, it should just flow.

Hope that is helpful.