Given that her base design is a pretty big shoutout to Samus, that's sort of intentional :)
I thought Riven was a dude for a very long time.
I thought Kayle was a guy the first time I saw her... then I noticed boobs. And I was all like "wtf what is this why aren't they falling out of her shirt like every other splash art"
That was me with Quinn
The first time I used her was a different story. I was like "is... is she magic...? is she AD? ...how"
I knew she was a female from the start. I seemed like the only one. People actually thought I was brain damaged before Unmasked because it was a guy. Then Unmasked came out and nobody questioned me since.
I actually thought Samus was a guy when I was like 9 years old
Before I started playing League, I saw Kayle and I thought "Dang, this character looks really badass and exciting" A couple months later, I got around to actually playing her. Right Click Simulator was a huge success.
It should be noted that shortly after this the Kayle mid hell began and that actually was fun while it lasted.
I remember with her old splash art haha. I was like to my lvl 30 friend (i was like lvl 3) "that guy is so cool, wait he's a guy right" and then he told me that Kayle is a female. i was so dissapointed :(
it's not the first time something like that's happened http://img2.wikia.nocookie.net/__cb20110603213451/metroid/images/6/60/Good_M1_ending.gif and it wont be the last :p
Kayle would be a stupid name for a guy.
I'm surprised
hasn't shown up (2014 Splash). Kayle and Vayne were the ones I was confused af with.

I still didn't get my Stargate gif! Im gonna sue you for extorsion!
Jk...
But i'm pretty sure it was clear that Kayle was a Woman..
I relate more with Kennen on this one. Totally thought he was female for the longest time. In fact I still sometimes use the wrong pronoun at times but it is not as bad as when I started.
When you found out Samus was a girl at the age of like 10 Oh how sad i was
Riven, Original Splash Art.