Boss denied vacation request 8 months ahead of request. How to use FMLA or leave time instead without getting in trouble?

My girlfriend's parents are super generous. As a Christmas gift, they purchased cruise ship tickets for all of us. The cruise is the first week of August 2025.

I put in my request on January 2, 2025. I was told today (Jan. 10) that it was denied because that is a busy month for our department. Last year, our department head stated that August is a blackout month for annual leave, but then took a week off in August to help her kids move.

So, in addition to looking for another job, I'm just curious if there might be a way to use FMLA or Annual/Sick leave to take my vacation anyway?

Do I push back officially? Do I go to HR?

Fuck this place. I like the people I work for, but this is bullshit.

Edit for clarification- I work for a state university, and I'm salaried. I have a preexisting medical condition, but upon reflection, I probably won't go down the FMLA route at this point.