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One mistake and you get mistaken for a troll and flamed.
Literal
One mistake [with-で] troll [and-と] mistaken-[passive-られて], flamed-[regret-てしまう].
インターネット culture vocabulary: 荒らし ('troll, vandal') literally means 'one who lays waste.' 叩かれる ('to be bashed/flamed') is the passive of 叩く 'to hit,' commonly used online for public criticism. 間違えられて is the passive of 間違える 'to mistake.' The sentence captures the unforgiving nature of online communities.