Literally means "Reflection!" (Right back at you? I'm not sure about this)
It's a kid's expression, like in English kids often go at each other repeating "Are too!" "Am not!" "Are too!" "Am not!" ~~
So it's kind of a way to say "You called me stupid? No that's you!"
반사요 (slightly polite form)
반사여 (net slang, kid's slang of -요, sarcasm)
ㅎㅎ (hehe, haha)