I'd be like, "...okay but theres literally anyone else" or "who hurt you"
he's like.... alright but boring as hell? His high point is death and slamming R in a teamfight.
QwQeQQQQQQQQQQQQQQQ AND SMASH THAT ULT BUTTON 
Different things for different folks. Plenty of people seem to think Janna is a boring shield bot, but I quite enjoy zipping around making clutch shields and disengages and so forth. (And really many people find most supports boring, but I enjoy many of them.)
The holy grail karthus ult->pentakill moment is inevitably a very strong allure for some players, although they may even enjoy the Q spam. (Lots of people [including myself] like AA based adcs too, and that's basically just right clicking. All just a matter of taste.)
Boring as hell?
I play him cause he's funny as hell. Those ults and kills while dead are hilarious. Add in the statue of karthus and I'll jungle with him to get off tilt in normals.
You dont find dying in the middle of the enemy team and getting a Pentakill to be fun?
The fuck is wrong with today's youth
And what do ADC's do? Right click, right click, right click....
Lets face it, this game needs the monotonous button mashers.
