Reporting for no reason?

Sometimes I don't really understand whats going on inside of peoples heads. First we got this jax in the enemy team which complained about our champs being op, and wanted to report us because... because. Because shaco is op. And the champs are given randomly. Logical. After we reported him, he was in our team, 'another reason to report you', and continued the same thing. My question: for what do I report this behaviour? We just stopped communicating with him after a while, so we can report him later. But what reason is this? Would really want to know :D Because he was lv 30 with just a few games in aram (ironically), i assume he got banned earlier from another account. Why do people go solo into aram games just to report others?
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