In everyday speech, 变态 is a strong insult meaning 'pervert' or 'freak'. In biology, it's a neutral scientific term meaning 'metamorphosis' (e.g. of insects). Context is everything.
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Calling someone 变态 is very offensive in Chinese. In slang it can also mean 'insanely good/intense' (这题变态难 = this question is insanely hard).
