Chiming in to share your pain Mario Kart pain. I experienced these douchebags and was gobsmacked! At first I thought I just really bad and/or unlucky, until it got so ridiculous that it was clear it was some kind of cheat/hack/exploit. Like others, I gave up shortly thereafter.
There is a semi-zombie thread of Doper friend codes here. (I’ll add mine a bit later when I can get to the game).
I don’t know if there is the critical mass where you can reliably find another Doper online. Mabye a Doper Kart Tournament?