I just recently turned 18 and I've informed my friend about my desire to transition at 15. She's never seemed to take it seriously and she's the only person who knows about it besides an old school counsellor.
She sometimes makes sneaky remarks about it to my sister (who doesn't know yet and I wouldn't like her to know until I am ready.) and on one occasion jokingly called me "he" before giving me this feigned look of "oops."
When I first told her she shrugged it off and said "you're going to be disappointed when you find out that having a d**k won't solve all of your issues." and while we were watching TV (Family Guy, the episode where Quagmire's dad transitions.) she mentioned that she found that "disgusting."
More recently she proposed the idea of going bra shopping with me as I apparently "need" more. I declined, even the mere thought of it making me feel dysphoric but she said "you're a woman, you should start acting like one." and I can't even describe how much that hurt me. I don't think she'll really take me seriously and I'm not so sure who else to reach out to at the moment.