The story
The earliest use may be from a joke post on the Internet in 1998. Attested in print as early as 2002 in Chuck Morse’s The Gramsci Factor, and later popularized by Maajid Nawaz in 2012.
Etymology from Wiktionary, CC BY-SA 4.0.
regressive left
Today it means: A characterization of the left which suggests that it paradoxically holds reactionary views by its tolerance of illiberal principles and ideologies (such as extremist Islamism) for the sake of multiculturalism and cultural relativism. Full definition →