Usually spread across social media and typically used as a insult to anyone who may be perceived as holding left-wing views. If the use of the term 'lefty' isn't backed up with any justification in an argument, it's a good indication they cannot form a rebuttal and only want to cease the argument. Further prodding after being called a 'lefty' usually results in being compared to a child, snowflake, stupid, degenerate, or anything which the initial user of the word 'lefty' isn't already.