This is easily abused, and ruined one of my season starts several seasons back. You can flag people for Harassment on the Achievements Leaderboard and Conquests Leaderboard. (You can’t do the same on the Greater Rift Leaderboards though). And for the first person to complete a conquest, their Battle Tag pops up in the chat window, and you can report on that also just as if they said something.
It also doesn’t take that many people reporting you for the automatic system to kick into effect. I.e. (If someone else is going after conquests, and gets a few people to flag you…)
And Blizzard’s status is it’s unappealable, and you’ll just get a generic form letter of how you should read the ToS and not violate their rules. This has happened to not just me, but a few others I know as well. So now, I use an alt account for season starts because of community abuse.