Ok so: I’m cis female but had this problem, in that I could never get them to cut my hair short enough. I eventually found ways to get them to cooperate though - and this was with hair I was sporting from 15-23, so you can probably get them to take you seriously. Keep in mind, though, that a lot of these tips will involve recognizing that you’ve already been misgendered and voluntarily running with that.
First of all, just go to a barbershop instead of a hair salon, if you can. It’s cheaper anyway, and you’re far more likely to get what you want from either a place where every employee has ten tattoos minimum, or from someone who’s mis-aging you not misgendering you
Barring that, e.g. If there’s only one shop nearby or your parents control where you go, pick the stylist with the wildest hair or most tattoos
If you can do so, make yourself sound like a huge lesbian the whole time. I could never get a middle aged white woman to actually take clippers my head if I hadn’t already talked about my (usually imaginary) girlfriend
If you like having your hair clipped/shaved, find out what numbers they use on you next time someone does it right, then tell everyone moving forward. Some still won’t believe you, but saying “I want a 2 into a 5” was always a lot more effective than “I want it shaved up”
Don’t tell them it’s fine until it is. I know this is something we’re socialized into accepting but this is true regardless of who you are and what hair cut you’re getting. If you’re not satisfied, say so. So what if they get annoyed? They’re not doing their job right. You’re paying for a service, you deserve it done the way you want.
On a related note, bribery will get you everywhere. If you live in a place where tipping is normal, and you can afford it, then come prepared with extra cash. If they do it right without you complaining, tip them well and say “hey, you’re the only stylist who’s actually listened, thank you.” If they need more convincing - especially if your parents are the ones paying and you know they’re trying not to piss them off - pull out a $10 or so and go “look, seriously, I will tip you extra if you just cut it boy-short”. It motivated a few ladies for me, when it was an option.
If all else fails, make up a reason you need it that short. You’re playing a character in the school play. You want to piss off your parents/ex/sister. Protest. “My friend has cancer and I want to make her feel less alone”. Yeah, lying sucks, but sometimes you gotta.
