Whenever that happens to me I end up getting destroyed by them. Urgh. I'm a casual player, but it's really demoralizing to be wiped out by a mirror because it pretty much means that you're going to be totally overshadowed in teamfights by them.
This is one of those gifs that didn't need to be a gif, lol.
"Cool! Mirror Match!"
(Me):"No it's not, I have a dino suit, you're not wearing one. This isn't a mirror match."
"So, this matters why?"
(Me):" Because, it proves I'm better than you."
"Wh-what? How?"
(M):"Because dinosaurs fucking rock."
(I usually dont say things like this because I end up eating my words.)
Who wore it better, league edition
I actually really like mirror match ups because this presents the opportunity to see how someone else uses the champion in the same role which presents a learning opportunity not only for yourself but for your opponent. Now this isn't as exciting on an ADC because build paths are generically the same, but for Jungle champions its more learning experience. However it does suck to get destroyed by your mirror as its been previously stated, I just look at it as more as a learning opportunity.
Then they stomp you
Fifth Age is the true master of penetration