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Loser
Negative Emotion
'Loser' often carries a strong negative feeling used to insult or criticize someone's ability. 
Informal Insult
'Loser' is informal and can be considered rude, so it's best used among friends jokingly. 
Self-Deprecation
People sometimes use 'loser' to humorously criticize themselves, often in a light-hearted way. 