It really gets to me when I come out as trans to someone and they go all "Really? You don't seem feminine at all!" Or something to that effect. I always awkwardly stumble out with something like "Yeah, cause I've been repressing it out of fear until recently..." And then at that point it's almost like they don't believe me. I know logically I shouldn't let it get to me cause I know who I am... but it's hard, you know? Has anyone else had experiences like that and gotten through them? If there are any thought tricks I'd appreciate them...
Well, what you've been telling people is perfectly valid. As a transguy, I've personally never been told that I don't seem masculine enough, even though I'm quite feminine. If it were to happen, I would probably explain that gender identity and gender expression aren't the same. There are plenty of cis/nontrans men that are feminine, and women who are masculine, but the difference is that they're comfortable with their assigned gender, whereas we're not. I think this is important for trans people to remember as well. As I'm sure you're aware, just because you've worn clothes from the boy's section or tried to conform to other stereotypes in the past doesn't mean you are or ever were a male, because actions don't determine your gender. It's how you feel inside. So, the only "thought trick" I can recommend is to keep in mind that gender identity is not equal to gender expression; while others can see the latter, you (and others, if they choose to believe you) know who you are, which is what's important. I'm not sure how helpful you'll find this, but that's the only advice I can offer.