Actual transpeople are annoyed by this since gender dysphoria is a life-ruining illness and not a fashion accessory.
Oh, there are a lot of trans people annoyed by it, but unfortunately, they're either drowned out, ignored, harassed, outright threatened, or deliberately misgendered for speaking up about it.
I am personally very supportive of people being who they know they're meant to be, and being able to be happy and comfortable with themselves (after all, our brains determine who we are, and the rest can be changed accordingly), but it seems like no one wants to acknowledge or talk about cis people who co-opt gender identity, as though they feel it will threaten the integrity of gender identity as a whole. No one wants to believe that there are people that would treat something so serious as a trend (kind of like you'd want to believe that no one would lie about things like being raped, being a victim of a national tragedy, or being a victim of a "Satanic" cult, but unscrupulous people have taken advantage of all of those things for personal gain), but you actually see it a lot these days, especially on places like tumblr.
I kind of get why they ignore it, as it would give bigots a reason to say, "See? It's all just a CHOICE! They're FAKING it for ATTENTION!!", but at the same time, I think such posturing lowers the value/meaning of being trans, and also seems insulting. I can't imagine going through life with crippling dysphoria, and having to deal with transphobia, hearing about hate crimes and trans people being murdered, and then some kid's like "I'm TRANS! Please refer to me as "bunself"! You don't need dysphoria to be trans!". To me, it just seems like...real trans people and their suffering are being USED.
I don't know. As I'm not trans, I try to stay out of it. I don't want to define anything for anyone else. I'm just going by what I've heard from trans people that are either in or have gone through hormone therapy, etc., and expressing my personal reaction. It just comes off as extremely disrespectful, and invasive. However, I don't know if I can blame the kids, considering how much seething hatred they see every day on tumblr for anyone that's cis, straight, white, etc. In that light, it makes sense that some would adopt identities that they can consider not cis/het, but without having to make actual financial/medical, or other life-changing commitment to. They can reassure themselves and others that the hatred doesn't apply to them, avoid further hate/harassment, and have their opinions on such matters actually be considered, rather than dismissed. They're young, so they take hateful comments much more to heart than the average adult. They're also looking for acceptance, and want to be the ones to "change the world" (and basically want to not be how they view older adults). I also can't blame those trans people that go along with it, because I feel like they just want younger people that are questioning themselves to not have to go through the same level of stress and confusion that they did. Nobody's truly wrong here, but it has inadvertently created a precarious and potentially harmful situation.
I just feel bad for everyone involved. Kids shouldn't have to feel that way just to be considered a decent human being, and trans people shouldn't have to deal with ANY of the shit they do, let alone this unhealthy climate that they're not even allowed to question or criticize without being disowned and harassed by the very community they should feel safest in.