Report for Tryhard. What?

I picked garen for a normal game and my enemy laner picks Bard. I get fed at this guy gets really salty saying "report tryhard" and stuff like that. I've been playing this game for 3 years and i've never heard this. Is this a common thing? I mean do people like that Bard even know this is a game. Can't i just play what i want just to have fun?
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