I would like to open this letter by acknowledging your One Direction prowess. Being able to identify which boy is which by a snapshot of their ankle is an important fangirl power well beyond me. But now I'd like to tell you something as important as that talent: I don't have to be as good as you to like them. I shouldn't be challenged with "What's Niall's middle name???" when I laugh at a "Niall ate _________" joke. (I Wikipedia'd it: His middle name is James.)
I don't need to burst into tears and drop whatever I'm doing whenever a song of theirs comes on. In fact, I don't even need to like all their music. I can just like three songs, and that's fine. You know why? Because I think the guys would prefer I love those three songs, rather than lukewarm sorta like all of them. It should be OK for me to say "I think the 1D guys are well fit" without someone demanding which I want to marry, and then wanting to attack me when I feebly offer the name of "MY Niall/Zayn/Harry/Liam/Louis." I'm not challenging your adoration, in fact, it's rather impressive. But please stop using your level of affection to measure someone elses "real fan"-ness.
And don't forget: you're cute as a button, every single one of you.
P.S. Anyone want to go see This Is Us with me?